Chapter VI (2)

In the case of the lakes of Norway and Sweden, there is independent evidence that they formerly communicated with the Baltic, and were, in fact, fiords or arms of the sea. The communication of these fiords with the sea having been gradually cut off, the marine animals they contained have been imprisoned; and as the water has been slowly changed from salt to fresh by the drainage of the surrounding land, only those which were able to withstand the altered conditions have survived. Among these is the _Mysis oculata_, which has in the meanwhile undergone the slight variation which has converted it into _Mysis relicta_. Whether the same explanation {328} applies to Lakes Superior and Michigan, or whether the _Mysis oculata_ has not passed into these masses of fresh water by channels of communication with the Arctic Ocean which no longer exist, is a secondary question. The fact remains that _Mysis relicta_ is a primitively marine animal which has become completely adapted to fresh-water life.

[39] See on this interesting subject: Martens, “On the
occurrence of marine animal forms in fresh water.” Annals of
Natural History, 1858: Lovèn. “Ueber einige im Wetter und Wener
See gefundene Crustaceen.” Halle Zeitschrift für die Gesammten
Wissenschaften, xix., 1862: G. O. Sars, “Histoire Naturelle des
Crustacés d’eau douce de Norvège,” 1867.

Several species of prawns (_Palæmon_) abound in our own seas. Other marine prawns are found on the coasts of North America, in the Mediterranean, in the South Atlantic and Indian Oceans, and in the Pacific as far south as New Zealand. But species of the same genus (_Palæmon_) are met with, living altogether in fresh water, in Lake Erie, in the rivers of Florida, in the Ohio, in the rivers of the Gulf of Mexico, of the West India Islands and of eastern South America, as far as southern Brazil, if not further; in those of Chili and those of Costa Rica in western South America; in the Upper Nile, in West Africa, in Natal, in the Islands of Johanna, Mauritius, and Bourbon, in the Ganges, in the Molucca and Philippine Islands, and probably elsewhere.

Many of these fluviatile prawns differ from the marine species not only in their great size (some attaining a foot or more in length), but still more remarkably in the vast development of the fifth pair of thoracic appendages. These are always larger than the slender fourth pair (which answer to the forceps of the crayfishes); and, in the males especially, they are very long and strong, and {329} are terminated by great chelæ, not unlike those of the crayfishes. Hence these fluviatile prawns (known in many places by the name of “Cammarons”) are not unfrequently confounded with true crayfishes; though the fact that there are only three pair of ordinary legs behind the largest, forceps-like pair, is sufficient at once to distinguish them from any of the _Astacidæ_.

Species of these large-clawed prawns live in the {330} brackish water lagoons of the Gulf of Mexico, but I am not aware that any of them have yet been met with in the sea itself. The _Palæmon lacustris_ (_Anchistia migratoria_, Heller) abounds in fresh-water ditches and canals between Padua and Venice, and in the Lago di Garda, as well as in the brooks of Dalmatia; but its occurrence in the Adriatic or the Mediterranean, which has been asserted, appears to be doubtful. So the Nile prawn, though very similar to some Mediterranean prawns, does not seem to be identical with any at present known.[40]

In all these cases, it appears reasonable to apply the analogy of the _Mysis relicta_, and to suppose that the fluviatile prawns are simply the result of the adaptive modification of species which, like their congeners, were primitively marine.

[40] Heller, “Die Crustaceen des südlichen Europas,” p. 259.
Klunzinger, “Ueber eine Süsswasser-crustacee im Nil,” with
the notes by von Martens and von Siebold: Zeitschrift für
Wissenschaftliche Zoologie, 1866.

But if the existing sea prawns were to die out, or to be beaten in the struggle for existence, we should have, scattered over the world in isolated river basins, more or less distinct species of freshwater prawns,[41] the areas inhabited by which might hereafter be indefinitely enlarged or diminished, by alteration in the elevation of the {331} land and by other changes in physical geography. And, indeed, under these circumstances, the freshwater prawns themselves might become so much modified, that, even if the descendants of their ancestors remained unchanged in structure and habits in the sea, the relationship of the two might no longer be obvious.

[41] This seems actually to have happened in the case of the
widely-spread allies and companions of the fluviatile prawns,
_Atya_ and _Caridina_. I am not aware that truly marine species
of these genera are known.

These considerations appear to me to indicate the direction in which we must look for a rational explanation of the origin of crayfishes and their present distribution.

I have no doubt that they are derived from ancestors which lived altogether in the sea, as the great majority of the _Mysidæ_ and many of the prawns do now; and that, of these ancestral crayfishes, there were some which, like _Mysis oculata_ or _Penæus brasiliensis_, readily adapted themselves to fresh water conditions, ascended rivers, and took possession of lakes. These, more or less modified, have given rise to the existing crayfishes, while the primitive stock would seem to have vanished. At any rate, at the present time, no marine crustacean with the characters of the _Astacidæ_ is known.

As crayfishes have been found in the later tertiaries of North America, we shall hardly err in dating the existence of these marine crayfishes at least as far back as the miocene epoch; and I am disposed to think that, during the earlier tertiary and later mesozoic periods, these _Crustacea_ not only had as wide a distribution as the Prawns and _Penæi_ have now, but were differentiated into two groups, one with the general characters of the {332} _Potamobiidæ_ in the northern hemisphere, and another, with those of the _Parastacidæ_, in the southern hemisphere.

The ancestral Potamobine form probably presented the peculiarities of the _Potamobiidæ_ in a less marked degree than any existing species does. Probably the four pleurobranchiæ were all equally well developed; the laminæ of the podobranchiæ smaller and less distinct from the stem; the first and second abdominal appendages less specialised; and the telson less distinctly divided. So far as the type was less specially Potamobine, it must have approached the common form in which _Homarus_ and _Nephrops_ originated. And it is to be remarked that these also are exclusively confined to the northern hemisphere.

The wide range and close affinity of the genera _Astacus_ and _Cambarus_ appear to me to necessitate the supposition that they are derived from some one already specialised Potamobine form; and I have already mentioned the grounds upon which I am disposed to believe that this ancestral Potamobine existed in the sea which lay north of the miocene continent in the northern hemisphere.

In the marine primitive crayfishes south of the equator, the branchial apparatus appears to have suffered less modification, while the suppression of the first abdominal appendages, in both sexes, has its analogue among the _Palinuridæ_, the headquarters of which are in the southern hemisphere. That they should have ascended {333} the rivers of New Zealand, Australia, Madagascar, and South America, and become fresh water _Parastacidæ_, is an assumption which is justified by the analogy of the fresh-water prawns. It remains to be seen whether marine _Parastacidæ_ still remain in the South Pacific and Atlantic Oceans, or whether they have become extinct.

* * * * *

In speculating upon the causes of an effect which is the product of several co-operating factors, the nature of each of which has to be divined by reasoning backwards from its effects, the probability of falling into error is very great. And this probability is enhanced when, as in the present case, the effect in question consists of a multitude of phenomena of structure and distribution about which much is yet imperfectly known. Hence the preceding discussion must rather be regarded as an illustration of the sort of argumentation by which a completely satisfactory theory of the ætiology of the crayfish will some day be established, than as sufficing to construct such a theory. It must be admitted that it does not account for the whole of the positive facts which have been ascertained; and that it requires supplementing, in order to furnish even a plausible explanation of various negative facts.

The positive fact which presents a difficulty is the closer resemblance between the Amur-Japanese crayfish and the East American _Cambari_, than between the {334} latter and the West American _Astaci_; and the closer resemblance between the latter and the Pontocaspian crayfish, than either bear to the Amur-Japanese form. If the facts had been the other way, and the West American and Amur-Japanese crayfish had changed places, the case would have been intelligible enough. The primitive Potamobine stock might then have been supposed to have differentiated itself into a western astacoid, and an eastern cambaroid form;[42] the latter would have ascended the American, and the former the Asiatic rivers. As the matter stands, I do not see that any plausible explanation can be offered without recourse to suppositions respecting a former more direct communication between the mouth of the Amur, and that of the North American rivers, in favour of which no definite evidence can be offered at present.

The most important negative fact which remains to be accounted for is the absence of crayfishes in the rivers of a large moiety of the continental lands, and in numerous islands. Differences of climatal conditions are obviously inadequate to account for the absence of crayfishes in Jamaica, when they are present in Cuba; for their absence in Mozambique, and the islands of Johanna and Mauritius, when they are present in Madagascar; and for their absence in the Nile, when they exist in Guatemala. {335}

[42] Just as there is an American form of _Idothea_ and an
Asiatic form in the Arctic ocean at the present day.

At present, I confess that I do not see my way to a perfectly satisfactory explanation of the absence of crayfishes in so many parts of the world in which they mighty _à priori_, be expected to exist; and I can only suggest the directions in which an explanation may be sought.

The first of these is the existence of physical obstacles to the spread of crayfishes, at the time at which the Potamobine and the Parastacine stocks respectively began to take possession of the rivers, some of which have now ceased to exist; and the second is the probability that, in many rivers which have been accessible to crayfishes, the ground was already held by more powerful competitors.

If the ancestors of the Potamobine crayfishes originated only among those primitive crayfishes which inhabited the seas north of the miocene continent, their present limitation to the south, in the old world, is as easily intelligible as is their extension southward, in the course of the river basins of Northern America as far as Guatemala, but no further. For the elevation of the Eurasiatic highlands had commenced in the miocene epoch, while the isthmus of Panama was interrupted by the sea.

With respect to the Southern hemisphere, the absence of crayfishes in Mauritius and in the islands of the Indian Ocean, though they occur in Madagascar, may be due to the fact that the former islands are of comparatively late volcanic origin; while Madagascar is the remnant of {336} a very ancient continental area, the oldest indigenous population of which, in all probability, is directly descended from that which occupied it at the beginning of the tertiary epoch. If Parastacine _Crustacea_ inhabited the southern hemisphere at this period, and subsequently became extinct as marine animals, their preservation in the freshwaters of Australia, New Zealand, and the older portions of South America may be understood. The difficulty of the absence of crayfishes in South Africa[43] remains; and all that can be said is, that it is a difficulty of the same nature as that which confronts us when we compare the fauna of South Africa in general with that of Madagascar. The population of the latter region has a more ancient aspect than that of the former; and it may be that South Africa, in its present shape, is of very much later date than Madagascar.

[43] But it must be remembered that we have as yet everything to
learn respecting the fauna of the great inland lakes and river
systems of South Africa.

With respect to the second point for consideration, it is to be remarked that, in the temperate regions of the world, the crayfishes are by far the largest and strongest of any of the inhabitants of freshwater, except the _Vertebrata_; and that while frogs and the like fall an easy prey to them, they must be formidable enemies and competitors even to fishes, aquatic reptiles, and the smaller aquatic mammals. In warm climates, however, not only the large prawns which have been mentioned, but _Atyæ_ {337} and fluviatile crabs (_Thelphusa_) compete for the possession of the freshwaters; and it is not improbable that under some circumstances, they may be more than a match for crayfishes; so that the latter might either be driven out of territory they already occupied, as _Astacus leptodactylus_ is driving out _A. nobilis_ in the Russian rivers; or might be prevented from entering rivers already tenanted by their rivals.

In connection with this speculation, it is worthy of remark that the area occupied by the fluviatile crabs is very nearly the same as that zone of the earth’s surface from which crayfish are excluded, or in which they are scanty. That is to say, they are found in the hotter parts of the eastern side of the two Americas, the West Indies, Africa, Madagascar, Southern Italy, Turkey and Greece, Hindostan, Burmah, China, Japan, and the Sandwich Islands. The large-clawed fluviatile prawns are found in the same regions of America, on both east and west coasts, in Africa, Southern Asia, the Moluccas, and the Philippine Islands; while the _Atyidæ_ not only cover the same area, but reach Japan, extend over Polynesia, to the Sandwich Islands, on the north, and New Zealand, on the south, and are found on both shores of the Mediterranean; a blind form (_Troglocaris Schmidtii_), in the Adelsberg caves, representing the blind _Cambarus_ of the caves of Kentucky.

* * * * *

The hypothesis respecting the origin of crayfishes {338} which has been tentatively put forward in the preceding pages, involves the assumption that marine Crustacea of the astacine type were in existence during the deposition of the middle tertiary formations, when the great continents began to assume their present shape. That such was the case there can be no doubt, inasmuch as abundant remains of Crustacea of that type occur still earlier in the mesozoic rocks. They prove the existence of ancient crustaceans, from which the crayfishes may have been derived, at that period of the earth’s history when the conformation of the land and sea were such as to admit of their entering the regions in which we now find them.

The materials which have, up to the present, time been collected are too scanty to permit of the tracing out of all the details of the genealogy of the crayfish. Nevertheless, the evidence which exists is perfectly clear, as far as it goes, and is in complete accordance with the requirements of the doctrine of evolution.

Mention has been made of the close affinity between the crayfishes and the lobsters—the _Astacina_ and the _Homarina_; and it fortunately happens that these two groups, which may be included under the common name of the _Astacomorpha_, are readily distinguishable from all the other _Podophthalmia_ by peculiarities of their exoskeleton which are readily seen in all well-preserved fossils. In all, as in the crayfish, there are large forceps, followed by two pairs of chelate ambulatory limbs, while {339} the succeeding two pairs of legs are terminated by simple claws. The exopodite of the last abdominal appendage is divided into two parts by a transverse suture. The pleura of the second abdominal somite are larger than the others, and overlap those of the first somite, which are very small. Any fossil crustacean which presents all these characters, is certainly one of the _Astacomorpha_.

The _Astacina_, again, are distinguished from the _Homarina_ by the mobility of the last thoracic somite, and the characters of the first and second abdominal appendages, when they are present; or by their entire absence. But it is so difficult to make out anything about either of these characters in fossils, that, so far as I am aware, we know nothing about them in any fossil Astacomorph. And hence, it may be impossible to say to which division any given form belongs, unless its resemblances to known types are so minute and so close as to remove doubt.

For the present purpose, the series of the fossiliferous rocks may be grouped as follows:—1. Recent and Quaternary. 2. Newer Tertiary (Pliocene and Miocene). 3. Older Tertiary (Eocene). 4. Cretaceous (Chalk, Greensand and Gault). 5. Wealden. 6. Jurassic (Purbeck to Inferior Oolite). 7. Liassic. 8. Triassic. 9. Permian. 10. Carboniferous. 11. Devonian. 12. Silurian. 13. Cambrian.

Now the oldest known member of the group of the {341} decapod _Podophthalmia_ to which the _Astacomorpha_ belong occurs in the Carboniferous formation. It is the genus _Anthrapalæmon_—a small and very curious crustacean, about which nothing more need be said at present, as it does not appear to have special affinities with the _Astacomorpha_. In the later formations, up to the top of the Trias, podophthalmatous _Crustacea_ are very rare; and, unless the Triassic genus _Pemphix_ is an exception, no Astacomorphs are known to occur in them. The specimens of _Pemphix_ which I have examined are not sufficiently complete to enable me to express any opinion about them.

The case is altered when we reach the Middle Lias. In fact this yields several forms of a genus, _Eryma_ (fig. 80, B), which also occurs in the overlying strata almost up to the top of the Jurassic series, and presents so many variations that nearly forty different species have been recognised. _Eryma_ is, in all respects, an Astacomorph, and so far as can be seen, it differs from the existing genera only in such respects as those in which they differ from one another. Thus it is quite certain that Astacomorphous _Crustacea_ have existed since a period so remote as the older part of the Mesozoic period; and any hesitation in admitting this singular persistency of type on the part of the crayfishes, is at once removed by the consideration of the fact that, along with _Eryma_, in the Middle Lias, prawn-like _Crustacea_, generically identical with the existing _Penæus_, flourished in the sea {342} and left their remains in the mud of the ancient sea bottom.

_Eryma_ is the only crustacean, which can be certainly ascribed to the _Astacomorpha_, that has hitherto been found in the strata from the Middle Lias to the lithographic slates; which last lie in the upper part of the Jurassic series. In the freshwater beds of the Wealden, no _Astacomorpha_ are known, and although no very great weight is to be attached to a negative fact of this kind, it is, so far, evidence that the _Astacomorpha_ had not yet taken to freshwater life. In the marine deposits of the Cretaceous epoch, however, astacomorphous forms, which {343} are known by the generic names of _Hoploparia_ and _Enoploclytia_, are abundant.

The differences between these two genera, and between both and _Eryma_, are altogether insignificant from a broad morphological point of view. They appear to me to be of less importance than those which obtain between the different existing genera of crayfishes.

_Hoploparia_ is found in the London clay. It therefore extends beyond the bounds of the Mesozoic epoch into the older Tertiary. But when this genus is compared with the existing _Homarus_ and _Nephrops_, it is found partly to resemble the one and partly the other. Thus, on one line, the actual series of forms which have succeeded one another from the Liassic epoch to the present day, is such as must have existed if the common lobster and the Norway lobster are the descendants of _Erymoid_ crustaceans which inhabited the seas of the Liassic epoch.

Side by side with _Eryma_, in the lithographic slates, there is a genus, _Pseudastacus_ (fig. 80, A), which, as its name implies, has an extraordinarily close resemblance to the crayfishes of the present day. Indeed there is no point of any importance in which (in the absence of any knowledge of the abdominal appendages in the males) it differs from them. On the other hand, in some features, as in the structure of the carapace, it differs from _Eryma_, much as the existing crayfishes differ from _Nephrops_. Thus, in the latter part of the Jurassic epoch, the Astacine type {344} was already distinct from the Homarine type, though both were marine; and, since _Eryma_ begins at least as early as the Middle Lias, it is possible that _Pseudastacus_ goes back as far, and that the common protastacine form is to be sought in the Trias. _Pseudastacus_ is found in the marine cretaceous rocks of the Lebanon, but has not yet been traced into the Tertiary formations.

I am disposed to think that _Pseudastacus_ is comparable to such a form as _Astacus nigrescens_ rather than to any of the _Parastacidæ_, as I doubt the existence of the latter group at any time in northern latitudes.

In the chalk of Westphalia (also a marine deposit) a single specimen of another Astacomorph has been discovered, which possesses an especial interest as it is a true _Astacus_ (_A. politus_, Von der Marck and Schlüter), provided with the characteristic transversely divided telson which is found in the majority of the _Potamobiidæ_.

If we arrange the results of palæontological inquiry which have now been stated in the form of a table such as that which is given on the following page, the significance of the succession of astacomorphous forms, in time, becomes apparent. {345}

SUCCESSIVE FORMS OF THE ASTACOMORPHOUS TYPE.

I. Recent. _Potamobiidæ._ _Homarina._ _Penæus._ ────────────────────────────────────|─────────────────|────────────────────|── II. Later Tertiary. _Astacus_ | | | (Idaho). | | | ────────────────────────|───────────|─────────────────|────────────────────|── III. Earlier Tertiary. | | _Hoploparia._ | ────────────────────────|───────────|──────────────────────────────────────|── IV. Cretaceous. _Astacus._ _Pseudastacus._ _Enoploclytia._ _Hoploparia._ | ────────────────────────────\─────────────────────────────/────────────────|── V. Wealden \ / | (Fresh Water). \ / | ───────────────────────────────\───────────────────────/───────────────────|── VI. Jurassic. _Pseudastacus._ _Eryma._ _Penæus._ ─────────────────────────────────|────────────────────|────────────────────|── VII. Liassic. | _Eryma._ _Penæus._ ────────────────────────────────────────────────────────────────────────────── VIII. Triassic. ────────────────────────────────────────────────────────────────────────────── IX. Permian. ────────────────────────────────────────────────────────────────────────────── X. Carboniferous. _Anthrapalæmon._ ────────────────────────────────────────────────────────────────────────────── XI. Devonian. ────────────────────────────────────────────────────────────────────────────── XII. Silurian. ────────────────────────────────────────────────────────────────────────────── XIII. Cambrian.

If an Astacomorphous crustacean, having characters intermediate between those of _Eryma_ and those of _Pseudastacus_, existed in the Triassic epoch or earlier; if it gradually diverged into Pseudastacine and Erymoid forms; if these again took on Astacine and Homarine {346} characters, and finally ended in the existing _Potamobiidæ_ and _Homarina_, the fossil forms left in the track of this process of evolution would be very much what they actually are. Up to the end of the Mesozoic epoch the only known _Potamobiidæ_ are marine animals. And we have already seen that the facts of distribution suggest the hypothesis that they must have been so, at least up to this time.

Thus, with respect to the Ætiology of the crayfishes, all the known facts are in harmony with the requirements of the hypothesis that they have been gradually evolved in the course of the Mesozoic and subsequent epochs of the world’s history from a primitive Astacomorphous form.

And it is well to reflect that the only alternative supposition is, that these numerous successive and coexistent forms of insignificant animals, the differences of which require careful study for their discrimination, have been separately and independently fabricated, and put into the localities in which we find them. By whatever verbal fog the question at issue may be hidden, this is the real nature of the dilemma presented to us not only by the crayfish, but by every animal and by every plant; from man to the humblest animalcule; from the spreading beech and towering pine to the _Micrococci_ which lie at the limit of microscopic visibility.

{347}

NOTES.

NOTE I., CHAPTER I., p. 17.

THE CHEMICAL COMPOSITION OF THE EXOSKELETON.

The harder parts of the exoskeleton of the crayfish contain rather more than half their weight of calcareous salts. Of these nearly seven-eighths consist of carbonate of lime, the rest being phosphate of lime.

The animal matter consists for the most part of a peculiar substance termed _Chitin_, which enters into the composition of the hard parts not only of the _Arthropoda_ in general but of many other invertebrated animals. Chitin is not dissolved even by hot caustic alkalies, whence the use of solutions of caustic potash and soda in cleaning the skeletons of crayfishes. It is soluble in cold concentrated hydrochloric acid without change, and may be precipitated from its solution by the addition of water.

Chitin contains nitrogen, and according to the latest investigations (Ledderhose, “Ueber Chitin und seine Spaltungs-produkte:” Zeitschrift für Physiologische Chemie, II. 1879) its composition is represented by the formula C_{15}H_{26}N_{2}O_{10} .

NOTE II., CHAPTER I., p. 29.

THE CRAB’S EYES, OR GASTROLITHS.

The “Gastroliths,” as the “crab’s eyes” may be termed, are found fully developed only in the latter part of the summer season, just before ecdysis sets in. They then give rise to rounded prominences, one on {348} each side of the anterior part of the cardiac division of the stomach. The proper wall of the stomach is continued over the outer surface of the prominence; and, in fact, forms the outer wall of the chamber in which the gastrolith is contained, the inner wall being formed by the cuticular lining of the stomach. When the outer wall is cut through, it is readily detached from the convex outer surface of the gastrolith, with which it is in close contact. The inner surface of the gastrolith is usually flat or slightly concave. Sometimes it is strongly adherent to the chitonous cuticula; but when fully formed it is readily detached from the latter. Thus the proper wall of the stomach invests only the outer face of the gastrolith, the inner face of which is adherent to, or at any rate in close contact with, the cuticula. The gastrolith is by no means a mere concretion, but is a cuticular growth, having a definite structure. Its inner surface is smooth, but the outer surface is rough, from the projection of irregular ridges which form a kind of meshwork. A vertical section shows that it is composed of thin superimposed layers, of which the inner are parallel with the flat inner surface, while the outer becomes gradually concentric with the outer surface. Moreover, the inner layers are less calcified than the outer, the projections of the outer surface being particularly dense and hard. In fact, the gastroliths are very similar to other hard parts of the exoskeleton in structure, except that the densest layers are nearest the epithelial substratum, instead of furthest away from it.

When ecdysis occurs, the gastroliths are cast off along with the gastric armature in general, into the cavity of the stomach, and are there dissolved, a new cuticle being formed external to them from the proper wall of the stomach. The dissolved calcareous matter is probably used up in the formation of the new exoskeleton.

According to the observations of M. Chantran (Comptes Rendus, LXXVIII. 1874) the gastroliths begin to be formed about forty days before ecdysis takes place in crayfish of four years’ old; but the interval is less in younger crayfish, and is not more than ten days during the first year after birth. When shed into the stomach during ecdysis they are ground down, not merely dissolved. The process of destruction and absorption takes twenty-four to thirty hours in very young crayfish, seventy to eighty hours in adults. Unless the gastroliths are normally developed and re-absorbed, ecdysis is not healthily effected, and the crayfish dies in the course of the process. {349}

According to Dulk (“Chemische Untersuchung der Krebsteine:” Müller’s Archiv. 1835), the gastroliths have the following composition:—

Animal matter soluble in water 11·43 Animal matter insoluble in water (probably chitin) 4·33 Phosphate of lime 18·60 Carbonate of lime 63·16 Soda reckoned as carbonate 1·41 ───── 98·93 ─────

The proportion of mineral to animal matter and of phosphate to carbonate of lime is therefore greater in the gastroliths than in the exoskeleton in general.

NOTE III., CHAPTER I., p. 31.

GROWTH OF CRAYFISH.

The statements in the text, after the words “By the end of the year,” regarding the sizes of the crayfish at different ages, are given on the authority of M. Carbonnier (L’Écrevisse. Paris, 1869); but they obviously apply only to the large “Écrevisse à pieds rouges” of France, and not to the English crayfish, which appears to be identical with the “Écrevisse à pieds blancs,” and is of much smaller size. According to M. Carbonnier (l. c. p. 51), the young crayfish just born is “un centimètre et demi environ,” that is to say, three-fifths of an inch long. The young of the English crayfish still attached to the mother, which I have seen, rarely exceeds half this length.

M. Soubeiran (“Sur l’histoire naturelle et l’education des Écrevisses:” Comptes Rendus, LX. 1865) gives the result of his study of the growth of the crayfishes reared at Clairefontaine, near Rambouillet, in the following table:

Mean length. Mean weight.
Metres. Grammes.

Crayfish of the year 0·025 0·50 Crayfish 1 year old 0·050 1·50 Crayfish 2 years old 0·070 3·50 Crayfish 3 years old 0·090 6·50 Crayfish 4 years old 0·110 17·50 Crayfish 5 years old 0·125 18·50 Crayfish indeterminate 0·160 30·00 Crayfish very old 0·190 125·00

These observations must also apply to the “Écrevisse à pieds rouges.”

{350}

NOTE IV., CHAPTER I., p. 37.

THE ECDYSES OF CRAYFISHES.

There is a good deal of discrepancy between different observers as to the frequency of the process of ecdysis in crayfishes. In the text I have followed M. Carbonnier, but M. Chantran (“Observations sur l’histoire naturelle des Écrevisses:” Comptes Rendus, LXXI. 1870, and LXXIII. 1871), who appears to have studied the question (on the “écrevisse à pieds rouges” apparently) very carefully, declares that the young crayfish moults no fewer than eight times in the course of the first twelve months. The first moult takes place ten days after it is hatched; the second, third, fourth, and fifth, at intervals of from twenty to twenty-five days, so that the young animal moults five times in the course of the ninety to one hundred days of July, August, and September. From the latter month to the end of April in the following year, no ecdysis takes place. The sixth takes place in May, the seventh in June, and the eighth in July. In the second year of its age, the crayfish moults five times, that is to say, in August and in September, and in May, June, and July following. In the third year, the crayfish commonly moults only twice, namely in July and in September. At a greater age than this, the females moult only once a year, from August to September; while the males moult twice, first in June and July; afterwards in August and September.

The details of the process of ecdysis are discussed by Braun, “Ueber die histologischen Vorgänge bei der Häutung von _Astacus fluviatilis_.” Würzburg Arbeiten, Bd. II.

NOTE V., CHAPTER I., p. 39.

REPRODUCTION IN CRAYFISHES.

The males are said to approach the females in November, December, and January, in the case of the French crayfishes. In England they certainly begin as early as the beginning of October, if not earlier. According to M. Chantran (Comptes Rendus, 1870), and M. Gerbe (Comptes Rendus, 1858), the male seizes the female with his pincers, throws her on her back, and deposits the spermatic matter, firstly, on the external plates of the caudal fin; secondly, on the thoracic sterna around the external openings of the oviducts. During this operation, the appendages of the two first abdominal somites are carried backwards, {351} the extremities of the posterior pair are inclosed in the groove of the anterior pair; and the end of the vas deferens becoming everted and prominent, the seminal matter is poured out, and runs slowly along the groove of the anterior appendage to its destination, where it hardens and assumes a vermicular aspect. The filaments of which it is composed are, in fact, tubular spermatophores, and consist of a tough case or sheath filled with seminal matter. The spoon-shaped extremity of the second abdominal appendage, working backwards and forwards in the groove of the anterior appendage, clears the seminal matter out of it, and prevents it from becoming choked.

After an interval which varies from ten to forty-five days, oviposition takes place. The female, resting on her back, bends the end of the abdomen forward over the hinder thoracic sterna, so that a chamber is formed into which the oviducts open. The eggs are passed into the chamber by one operation, usually during the night, and are plunged into a viscous greyish mucus with which it is filled. The spermatozoa pass out of the vermicular spermatophores, and mix with this fluid, in which the peculiarity of their form renders them readily recognisable. The spermatozoa are thus brought into close relation with the ova, but what actually becomes of them is unknown.

The origin of the viscous matter which fills the abdominal chamber when the eggs are deposited in it, and the manner in which these become fixed to the abdominal limbs is discussed by Lereboullet (“Recherches sur le mode de fixation des œufs aux faux pattes abdominaux dans les Écrevisses.” Annales des Sciences Naturelles, 4e Ee. T. XIV. 1860), and by Braun (Arbeiten aus dem Zoologisch-Zootomischen Institut in Würzburg, II.).

NOTE VI., CHAPTER I., p. 42.

ATTACHMENT OF THE YOUNG CRAYFISH TO THE MOTHER.

I observe that I had overlooked a passage in the Report on the award of the Prix Montyon for 1872, Comptes Rendus, LXXV. p. 1341, in which M. Chantran is stated to have ascertained that the young crayfishes fix themselves “en saisissant avec un de leurs pinces le filament qui suspend l’œuf à une fausse patte de la mère.”

In the paper already cited from the Comptes Rendus for 1870, M. Chantran states that the young remain attached to the mother during ten days after hatching, that is to say, up to the first moult. Detached before this period, they die; but after the first moult, they sometimes leave the {352} mother and return to her again, up to twenty-eight days, when they become independent.

In a note appended to M. Chantran’s paper, M. Robin states, that “the young are suspended to the abdomen of the mother by the intermediation of a chitinous hyaline filament, which extends from a point of the internal surface of the shell of the egg as far as the four most internal filaments of each of the lobes of the median membranous plate of the caudal appendage. The filaments exist when the embryos have not yet attained three-fourths of their development.” Is this a larval coat? Rathke does not mention it and I have seen nothing of it in those recently hatched young which I have had the opportunity of examining.

NOTE VII., CHAPTER II., p. 64.

THE “SALIVARY” GLANDS AND THE SO-CALLED “LIVER” OF THE CRAYFISH.

Braun (Arbeiten aus dem Zoologisch-Zootomischen Institut in Würzburg, Bd. II. and III.) has described “salivary” glands in the walls of the œsophagus, in the metastoma, and in the first pair of maxillæ of the crayfish.

Hoppe-Seyler (Pflügers Archiv, Bd. XIV. 1877) finds that the yellow fluid ordinarily found in the stomachs of crayfishes always contains peptone. It dissolves fibrin readily, without swelling it up, at ordinary temperatures; more quickly at 40° Centigrade. The action is delayed by even a trace of hydrochloric acid, and is stopped by the addition of a few drops of water containing 0.2 per cent. of that acid. By adding alcohol to the yellow fluid, a precipitate is obtained, which is soluble in water and in glycerine. The aqueous solution of the precipitate has a strong digestive action on fibrin, which is arrested by acidulation with hydrochloric acid. These reactions show that the fluid is very similar to, if not identical with, the pancreatic fluid of vertebrates.

The secretion of the “liver” taken directly from that gland, has a more strongly acid reaction than the fluid in the stomach, but has similar digestive properties. So has an aqueous extract of the gland, and a watery solution of the alcoholic precipitate. The aqueous extract also possesses a strong diastatic action on starch, and breaks up olive oil. There is no more glycogen in the “liver” than is to be found in other organs, and no constituents of true bile are to be met with.

{353}

NOTE VIII., CHAPTER II., p. 81.

ANAL RESPIRATION IN CRAYFISH.

Lereboullet (“Note sur une respiration anale observée chez plusieurs Crustacés;” Mémoires de la Société d’Histoire Naturelle de Strasbourg, IV. 1850) has drawn attention to what he terms “anal respiration” in young crayfish, in which he observed water to be alternately taken into and expelled from the rectum fifteen to seventeen times in a minute. I have never been able to observe anything of this kind in the uninjured adult animal, but if the thoracic ganglia are destroyed, a regular rhythmical dilatation and closing of the anal end of the rectum at once sets in, and goes on as long as the hindermost ganglia of the abdomen retain their integrity. I am much disposed to imagine that the rhythmical movement is inhibited, when the uninjured crayfish is held in such a position that the vent can be examined.

NOTE IX., CHAPTER II., p. 82.

THE GREEN GLAND.

The existence of guanin in the green gland rests on the authority of Will and Gorup-Besanez (Gelehrte Anzeigen, d. k. Baienzschen Akademie, No. 233, 1848), who say that in this organ and in the organ of Bojanus of the freshwater mussel, they found “a substance the reactions of which with the greatest probability indicate guanin,” but that they had been unable to obtain sufficient material to give decisive results.

Leydig (Lehrbuch der Histologie, p. 467) long ago stated that the green gland consists of a much convoluted tube containing granular cells disposed around a central cavity. Wassiliew (“Ueber die Niere des Flusskrebses:” Zoologischer Anzeiger, I. 1878) supports the same view, giving a full account of the minute structure of the organ, and comparing it with its homologues in the _Copepoda_ and _Phyllopoda_.

NOTE X., CHAPTER III., p. 105.

THE ANATOMY OF THE NERVOUS SYSTEM OF THE CRAYFISH.

The details respecting the origin and the distribution of the nerves are intentionally omitted. See the memoir by Lemoine of which the title is given in the “Bibliography.”

{354}

NOTE XI., CHAPTER III., p. 110.

THE FUNCTIONS OF THE NERVOUS SYSTEM OF THE CRAYFISH.

Mr. J. Ward, in his “Observations on the Physiology of the Nervous System of the Crayfish,” (Proceedings of the Royal Society, 1879) has given an account of a number of interesting and important experiments on this subject.

* * * * *

NOTE XII., CHAPTER III., p. 124.

THE THEORY OF MOSAIC VISION.

Oscar Schmidt (“Die Form der Krystalkegel im Arthropoden Auge:” Zeitschrift für Wissenschaftliche Zoologie, XXX. 1878) has pointed out certain difficulties in the way of the universal application of the theory of mosaic vision in its present form, which are well worthy of consideration. I do not think, however, that the substance of the theory is affected by Schmidt’s objections.

NOTE XIII., CHAPTER III., p. 135.

THE SPERMATOZOA.

Since the discovery of the spermatozoa of the crayfish in 1835–36 by Henle and von Siebold. the structure and development of these bodies have been repeatedly studied. The latest discussion of the subject is contained in a memoir of Dr. C. Grobben (“Beiträge zur Kenntniss der männlichen Geschlechtsorgane der Dekapoden:” Wien, 1878). There is no doubt that the spermatozoon consists of a flattened or hemispherical body, produced at its circumference into a greater or less number of long tapering curved processes (fig. 34 F). In the interior of this are two structures, one of which occupies the greater part of the body, and, when the latter lies flat, looks like a double ring. This may be called, for distinctness’ sake, the _annulate corpuscle_. The other is a much smaller _oval corpuscle_, which lies on one side of the first. The annulate corpuscle is dense, and strongly refracting; the oval corpuscle is soft, and less sharply defined. Dr. Grobben describes the annulate corpuscle as “napfartig,” or cup-shaped; closed below, open above, and with the upper edge turned inwards, and applied to the inner side of the wall of the cup. It appeared to me, on the other hand, that the annulate corpuscle is really a hollow ring, somewhat {355} like one of the ring-shaped air-cushions one sees, on a very small scale. Dr. Grobben describes the spermatoblastic cells of the testis and their nuclear spindles; but his account of the development of the spermatozoa does not agree with my own observations, which, so far as they have gone, lead me to infer that the annulate corpuscle of the spermatozoon is the metamorphosed nucleus of the cell from which the spermatozoon is developed. For want of material, however, I was unable to bring my investigations to a satisfactory termination, and I speak with reserve.

NOTE XIV., CHAPTER IV., p. 174.

THE MORPHOLOGY OF THE CRAYFISH.

The founder of the morphology of the _Crustacea_, M. Milne Edwards, counts the telson as a somite, and consequently considers that twenty-one somites enter into the composition of the body in the _Podophthalmia_. Moreover, he assigns the anterior seven somites to the head, the middle seven to the thorax, and the hinder seven to the abdomen. There is a tempting aspect of symmetry about this arrangement; but as to the limits of the head, the natural line of demarcation between it and the thorax seems to me to be so clearly indicated between the somite which bears the second maxillæ and that which carries the first maxillipedes in the _Crustacea_, and between the homologous somites in Insects, that I have no hesitation in retaining the grouping which I have for many years adopted. The exact nature of the telson needs to be elucidated, but I can find no ground for regarding it as the homologue of a single somite.

It will be observed that these differences of opinion turn upon questions of grouping and nomenclature. It would make no difference to the general argument if it were admitted that the whole body consists of twenty-one somites and the head of seven.

NOTE XV., CHAPTER IV., p. 199.

THE HISTOLOGY OF THE CRAYFISH.

In dealing with the histology of the crayfish I have been obliged to content myself with stating the facts as they appear to me. The discussion of the interpretations put upon these facts by other observers, especially in the case of those tissues, such as muscle, on which there is as yet no complete agreement even as to matters of observation, would require a whole treatise to itself.

{356}

NOTE XVI., CHAPTER IV., p. 221.

THE DEVELOPMENT OF THE CRAYFISH.

The remark made in the last note applies still more strongly to the history of the development of the crayfish. Notwithstanding the masterly memoir of Rathke, which constitutes the foundation of all our knowledge on this subject; the subsequent investigations of Lereboullet; and the still more recent careful and exhaustive works of Reichenbach and Bobretsky, a great many points require further investigation. In all its most important features I have reason to believe that the account of the process of development given in the text, is correct.

NOTE XVII., CHAPTER VI., p. 297.

PARASITES OF CRAYFISHES.

In France and Germany crayfishes (apparently, however, only _A. nobilis_) are infested by parasites, belonging to the genus _Branchiobdella_. These are minute, flattened, vermiform animals, somewhat like small leeches, from one-half to one-third of an inch in length, which attach themselves to the under side of the abdomen (_B. parasitica_), or to the gills (_B. astaci_), and live on the blood and on the eggs of the crayfish. A full account of this parasite, with reference to the literature of the subject, is given by Dormer (“Ueber die Gattung Branchiobdella:” Zeitschrift für Wiss. Zoologie, XV. 1865). According to Gay, a similar parasite is found on the Chilian crayfish. I have never met with it on the English crayfish. The Lobster has a somewhat similar parasite, _Histriobdella_. Girard, in the paper cited in the Bibliography, gives a curious account of the manner in which the little lamellibranchiate mollusk, _Cyclas fontinalis_, shuts the ends of the ambulatory limbs of crayfishes which inhabit the same waters, between its valves, so that the crayfish resembles a cat in walnut shells, and the pinched ends of the limbs become eroded and mutilated.

{357}

BIBLIOGRAPHY.

The subjoined list indicates the chief books and memoirs, in addition to those mentioned in the text and in the Appendix, which may be advantageously consulted by any one who wishes to study more fully the biology of the crayfishes.

I.—NATURAL HISTORY.

ROESEL VON ROSENHOF. Der Monatlich-herausgegeben Insekten Belustigung. 1755.

CARBONNIER. L’Écrevisse, Paris, 1869.

BRANDT AND RATZEBURG. Medizinische Zoologie. Bd. II., pp. 58–70.

BELL. British Stalk-eyed Crustacea, 1853.

SOUBEIRAN. Sur l’Histoire naturelle et l’Éducation des Écrevisses. Comptes Rendus, LX., 1865.

CHANTRAN. Observations sur l’Histoire naturelle des Écrevisses. Comptes Rendus, LXXI., 1870.

—— Sur la Fécondation des Écrevisses. Ibid., LXXIV., 1872.

—— Expériences sur la Régénération des Yeux chez les Écrevisses. Ibid., LXXVII., 1873.

—— Observations sur la Formation des Pierres chez les Écrevisses. Ibid., LXXVIII., 1874.

—— Sur le Mécanisme de la Dissolution intrastomacale des Concrétions gastriques des Écrevisses. Ibid., LXXVIII., 1874.

STEFFENBERG. Bijdrag til kanne domen on flodkraftens natural historia, 1872. Abstract in Zoological Record, IX.

VALLOT. Sur l’Écrevisse fluviatile et sur son parasite l’Astacobdelle branchiale. Comptes Rendus Acad. Sciences, Dijon. Mémoires, 1843–44. Dijon, 1845.

PUTNAM. On some of the Habits of the Blind Crayfish. Proceedings Boston Society of Nat. History, XVIII. {358}

HELLER. Ueber einen Flusskrebs-albino. Verhand d. Z. Bot. Gesellschaft, Wien. Bd. 7, 1857, and Bd. 8, 1858.

LEREBOULLET. Sur les variétés Rouge et Bleue de l’Écrevisse fluviatile. Comptes Rendus, XXXIII., 1857.

GIRARD. Quelques Remarques sur l’Astacus fluviatilis. Ann. Soc. Entom. France, T. VII. 1859.

II.—ANATOMY AND PHYSIOLOGY.

BRANDT AND RATZEBURG. _Op. cit._

MILNE EDWARDS. Histoire naturelle des Crustacés. 1834.

ROLLESTON. Forms of Animal Life. 1870.

HUXLEY. Manual of the Anatomy of Vertebrated Animals. 1877.

HUXLEY AND MARTIN. Elementary Biology. 1875.

SUCKOW. Anatomisch-Physiologische Untersuchungen. 1818.

KROHN. Verdauungsorgane des Krebses. Gefässsystem des Flusskrebses. Isis, 1834.

VON BAER. Ueber die sogenannte Erneuerung des Magens der Krebse und die Bedeutung der Krebssteine. Müller’s Archiv, 1835.

OESTERLEN. Ueber den Magen des Flusskrebses. Müller’s Archiv, 1840.

T. J. PARKER. On the Stomach of the Freshwater Crayfish. Journal of Anatomy and Physiology, 1876.

BARTSCH. Die Ernährungs- und Verdauungsorgane des _Astacus leptodactylus_. Budapester Naturhistor. Hefte II. 1878.

DESZŎ. Ueber das Herz des Flusskrebses und des Hummers. Zoologischer Anzeiger, I. 1878.

LEREBOULLET. Note sur une Respiration anale observée chez plusieurs Crustacées. Mém. de la Société d’Histoire Naturelle de Strasbourg, IV., 1850.

WASSILIEW. Ueber die Niere des Flusskrebses. Zoologischer Anzeiger, I. 1878.

LEMOINE. Recherches pour servir à l’histoire des systèmes nerveux, musculaire et glandulaire de l’Écrevisse. Annales des Sciences Naturelles, Sé. IV. T. 15, 1861.

DIETL. Die Organization des Arthropoden Gehirns. Zeitschrift für Wiss. Zoologie, XXVII., 1876.

KRIEGER. Ueber das centrale Nervensystem des Flusskrebses. Zoologischer Anzeiger, I., 1878.

LEYDIG. Das Auge der Gliederthiere. 1864. {359}

MAX SCHULZE. Die Zusammengesetzten Augen der Krebse und Insekten, 1868.

BERGER. Untersuchungen über den Bau des Gehirns und der Retina der Arthropoden. 1878.

GRENACHER. Untersuchungen über das Sehorgan der Arthropoden. 1879.

O. SCHMIDT. Die Form der Krystalkegel im Arthropoden Auge. Zeitschrift für Wiss. Zoologie, XXX., 1878.

FARRE. On the organ of hearing in the Crustacea. Phil. Trans. 1843.

LEYDIG. Ueber Geruchs- und Gehörorgane der Krebse und Insekten. Müller’s Archiv, 1860.

HENSEN. Studien über das Gehörorgan der Decapoden. Zeitschrift für Wissenschaftliche Zoologie, XIII. 1863.

GROBBEN. Beiträge zur Kenntniss der männlichen Geschlechtsorgane der Dekapoden. 1878.

BROCCHI. Recherches sur les Organes génitaux mâles des Crustacés décapodes. Annales des Sciences Naturelles, Sé. VI. ii.

LEYDIG. Zur feineren Bau der Arthropoden. Müller’s Archiv, 1855.

—— Handbuch der Histologie. 1857.

HAECKEL. Ueber die Gewebe des Flusskrebses. Müller’s Archiv, 1857.

BRAUN. Ueber die histologischen Vorgänge bei der Häutung von Astacus fluviatilis. Würzburg Arbeiten, II.

BAUR. Ueber den Bau der Chitinsehne am Kiefer des Flusskrebses und ihr Verhalten beim Schalenwechsel. Reichert u. Du Bois Archiv, 1860.

COSTE. Faits pour servir à l’Histoire de la Fécondation chez les Crustacés. Comptes Rendus, XLVI. 1858.

LEREBOULLET. Recherches sur la mode de Fixation des Œufs aux fausses pattes abdominales dans les Écrevisses. Annales des Sciences Naturelles, Sé. IV. T. 14, 1860.

III—DEVELOPMENT.

RATHKE. Ueber die Bildung und Entwickelung des Flusskrebses, 1829.

LEREBOULLET. Recherches d’Embryologie comparée sur le développement du Brochet, de la Perche et de l’Écrevisse. 1862. {360}

BOBRETSKY. (A Memoir in Russian, of which an abstract is given in Hofmann and Schwalbe, Jahresbericht für 1873 (1875)).

REICHENBACH. Die Embryonanlage und erste Entwickelung des Flusskrebses. Zeitschrift für Wiss. Zoologie. 1877.

IV.—TAXONOMY AND DISTRIBUTION OF CRAYFISHES.

A. _General._

MILNE EDWARDS. _Op. cit._

ERICHSON. Uebersicht der Arten der Gattung _Astacus_. Wiegmann’s Archiv für Naturgeschichte, XII. 1846.

DANA. Crustacea of the United States Exploring Expedition. 1852.

DE SAUSSURE. Note carcinologique sur la Famille des Thalassinides et sur celle des Astacides. Rev. et Magazin de Zoologie, IX.

HUXLEY. On the Classification and the Distribution of the Crayfishes. Proceedings of the Zoological Society. 1878.

B. _European and Asiatic._

RATHKE. Zur Fauna der Krym. 1836.

GERSTFELDT AND KESSLER. Cited in the text.

DE HAAN. Fauna Japonica. 1850.

LEREBOULLET. Description de deux nouvelles Espèces d’Écrevisses (_A. longicornis, A. pallipes_). Mém. Soc. Science Nat. Strasbourg. V. 1858.

HELLER. Crustaceen des südlichen Europa. 1863.

KESSLER. Ein neuer russischer Flusskrebs, _Astacus colchicus_. Bulletin de la Soc. Imp. des Naturalistes de Moscou, L. 1876.

C. _American._

STIMPSON. Crustacea and Echinodermata of the Pacific shores of North America. Journal of Boston Society of Natural History VI.; 1857–8.

DE SAUSSURE. Mémoire sur divers Crustacées nouveaux des Antilles et du Méxique. Mém. de la Société de Physique de Genève T. XIV., 1857.

VON MARTENS. Südbrasilische Süss- und Brackwasser Crustaceen (_A. pilimanus, A. brasiliensis_), Wiegmann’s Archiv, XXXV., 1869.

——. Ueber Cubansche Crustaceen. _Ibid._ XXXVIII.

HAGEN. Monograph of the North American _Astacidæ_. 1870. {361}

D. _Madagascar._

AUDOUIN AND MILNE EDWARDS. Sur une Espèce nouvelle du genre Écrevisse (_Astacus_). Écrevisse de Madagascar (_A. Madagascariensis_)., Mém. du Muséum d’Hist. naturelle, T. II. 1841.

E. _Australia._

VON MARTENS. On a new Species of _Astacus_. Annals & Mag. of Natural History, 1866.

HELLER. Reise der “Novara.” Zool. Theil. Bd. II. 1865.

F. _New Zealand._

MIERS. Notes on the Genera _Astacoides_ and _Paranephrops_. Transactions of the New Zealand Institute, IX., 1876.

—— _Paranephrops._ Zoology of “Erebus” and “Terror,” 1874. Catalogue of New Zealand Crustacea, 1876.

—— Annals of Natural History, 1876.

WOOD-MASON. On the mode in which the Young of the New Zealand _Astacidæ_ attach themselves to the Mother. Ann. & Mag. Natural History, 1876.

G. _Fossil Astacomorpha._

OPPEL. Palæontologische Mittheilungen, 1862.

BELL. British Fossil Crustacea. Palæontographical Society.

P. VAN BENEDEN. Sur la Découverte d’un Homard fossile dans l’Argile de Rupelmonde. Bulletin de l’Acad. Royale de Belgique. XXXIII., 1872.

VON DER MARCK UND SCHLÜTER. Neue Fische und Krebse von der Kreide von Westphalen. Palæontologica, XV. 1865.

COPE. On three extinct _Astaci_ from the freshwater tertiary of Idaho. Proceedings of the American Philosophical Society, XI., 1869–70.

{363}

INDEX.

A.

Abdomen, 19, 141
development of, 213

Abdominal appendages, 143
development of, 217

Abdominal somite, characters of, 142

Ætiology, 47

AGASSIZ, 308

Alimentary canal, 51
development of, 213, 222

Ambulatory legs, 168

American Crayfishes, 243, 247

_Amœba_, 285

Amurland Crayfishes, 304

Antenna, 23, 172
development of, 214, 218

Antennule, 23, 173
development of, 214, 218

_Anthrapalæmon_, 341

Anus, 29

Apodeme, 99, 158, 175

Appendage, 24, 143, 161, 173
abdominal, 143
cephalic, 170
thoracic, 164

Archenteron, 211

Arctogæal province, 314

Areola, 235

ARISTOTLE, referred to, 4

Arteries, 71

Arteries, development of, 224

Arthrobranchia, 75

Arthrophragm, 158

_Arthropoda_, 279, 284

Articulations, 95

Asiatic Crayfishes, 304

_Astacina_, 254

_Astacoides_, 250, 313

_Astacomorpha_, 338

_Astacopsis_, 250, 264

_Astacus_, division into sub-genera, 290

_Astacus angulosus_, 302, 310
_colchicus_, 302, 310
_dauricus_, 304, 310
_fluviatilis_,
anatomy, general account of, 17–31
attachment of young to mother, 40, 351
branchial formula, 266
development, 205–226
distribution, geographical 44, 288, 298
distribution, chronological, 44
ecdysis, 32, 350
general characters, 6
growth, 31, 349
habits, 8 {364}
histology, 174
mortality, 127
muscular system, 90
myths concerning, 44
name, origin of, 13
nervous system, 101
newly hatched young, characters of, 219
nutrition, 48
occurrence, 5, 8
organs of alimentation, 51
circulation, 68
excretion, 82, 353
hearing, 116
reproduction, 128
respiration, 75, 353
sight, 118
smell, 114
taste, 115
touch, 113
prehension of food, 49
putrid, effect of smell of, 45
reproduction of lost limbs, 38
reproduction, sexual, 39, 128, 135, 350
sexual characters, 7, 20, 32, 145, 241
somites and appendages, 143
systematic description, 230
use as food, 10, 289
varieties, 289
_fontinalis_, 290
_japonicus_, 304
_klamathensis_, 305
_leniusculus_, 305
_leptodactylus_, 299, 302, 303, 310, 320
_nigrescens_, 244
_nobilis_, 290, 295, 296, 299, 310
_oreganus_, 305
_pachypus_, 302, 310
_pallipes_, 290
_politus_, 344
_saxatilis_, 290
_Schrenckii_, 304, 310
_torrentium_, 290, 294, 298, 310, 311
_tristis_, 290
_Trowbridgii_, 305

_Atya_, _Atyidæ_, 331, 336

Auditory organ, 116
setæ, 116

Australian Crayfishes, 306
province, 314

Austrocolumbian province, 314

_Axius_, 271

B.

Ball, R., quoted, 36

Basipodite, 143

BELL, T., quoted, 37, 42

Bile-duct, 61, 66