Chapter CIX: Section 16: The uro-genital organs of the frog, and especially those

of the male, correspond with embryonic stages of the rabbit. In this sex the testes (T., Sheet 13) lie in the body cavity, and are white bodies usually dappled with black pigment. Vasa efferentia (v.e.) run to the internal border of the anterior part of the kidney, which answers, therefore, to the rabbit's epididymis. The hinder part of the kidney is the predominant renal organ. There is a common uro-genital duct, into which a seminal vesicle, which is especially large in early spring, opens. This is the permanent condition of the frog. In the rabbit, for urogenital duct, we have ureter and vas deferens; the testes and that anterior part of the primitive kidney, the epididymis, shift back into the scrotal sacs, and the ureters shift round the rectum and establish a direct connection with the bladder, carrying the genital ducts looped over them. The oviducts of the female do not fuse distally to form a median vagina as they do in the rabbit. In front of the genital organ in both sexes is a corpus adiposum (c.ad.), which acts as a fat store, and is peculiar to the frogs and toads. The distal end of the oviduct of the female is in the breeding season (early March) enormously distended with ova, and the ovaries become then the mere vestiges of their former selves. The distal end of the oviduct is, therefore, not unfrequently styled the uterus. There is no penis in the male, fertilisation of the ova occurring as they are squeezed out of the female by the embracing fore limbs of the male. The male has a pad, black in winter, shown in Figure 1, which is closely pressed against the ventral surface of the female in copulation, and which serves as a ready means of distinguishing the sex.

Section 17. The spinal cord has a general similarity to that of the rabbit; the ratio of its size to that of the brain is larger, and the nerves number ten pairs altogether. The first of these (sp. 1, in Figure 2, Sheet -12- ) {First Edition error.} [13] corresponds in distribution with the rabbit's hypoglossal nerve, a point we shall refer to again when we speak of the skull. The second and third constitute the brachial plexus. The last three form the sciatic plexus going to the hind limb.