402 Vertebrata. 



tlius takes place in the water. The fore limbs are stronger in the 

 males than in the females, and in many forms are furnished, in 

 the breeding season, with rough horny warts, especially on the 

 hands, so that they can grip more firmly. The male U r o d e 1 e 

 deposits the spermatophores, which consist of masses of jelly 

 containing spermatozoa, and vary in form, at the bottom of the 

 ■watQT. The female then moves over them, so that they become 

 attached to the cloacal opening; they are taken into the cloaca 

 where the spermatozoa penetrate into little sacs in the wall, which 

 serve as receptacula seminis. Here fertilisation occurs within the body 

 of the female. 



As already mentioned, there is, in the Toads (Bufo), at the anterior end of 

 the testis, a small body, which i-esembles an unripe ovary in stnicture. In 

 the females of this genus, a coiTesponding portion of the ovai-y is similarly 

 developed ; it is especially noticeable in young females, but degenerates later. 



A pair of yellow bodies containing fat, and often very conspicuous, is attached 

 to the reproductive glands in Amphibia, and is frequently in close connection 

 with them. These are the so-called fat bodies, which are digitifoi-m in 

 Anura, and originate by modification of a poi-tion of the ovary or testis. 



The eggs are usually laid in fresh water, surrounded by a thin 

 albuminous coat, which swells up in the water to a thick gelatinous 

 capsule. They are either laid singly (rarely) or in rows, strings, or 

 masses. They vary in size from two to about ten m/m. in diameter. 

 Segmentation is usually total, but the segmentation spheres are 

 larger at one pole (c/., p. 45, and Fig. 34) ; the larger eggs, how- 

 ever, undergo partial segmentation. Rarely, as in the Salamander, 

 the ovum develops within the oviduct. The eggs or brood are 

 protected in various Amphibia : Pipa, Alytes ohstetrieans, Ccecilia, 

 etc. (see below). 



The metamorphosis, which all Amphibia undergo, is 

 specially characteristic of the group. The larvee, as already men- 

 tioned, are provided with well-developed gills ; the circulation and 

 the disposition of the vascular system are almost identical with 

 those of Pish ; lungs are already present, but have as yet no re- 

 spiratory function. At the metamorphosis a significant change 

 in structure and mode of life occurs; the gills atrophy and the 

 lungs become functional, involving amongst other alterations, great 

 modifications in the vascular system (c/. p. 400). The differences 

 between larva and adult are not, however, confined to these; in 

 many other respects the former approaches the piscine type; for 

 instance, there is no stratum corneum ; lateral line organs are 

 present; they always lie free, and even bear delicate cylinders like 

 those of Fish.* Eyelids are absent ; a continuous fin is present at 

 first, but disappears in later larval life, and the visceral skeleton is 



* The sensory papillse also occur in adult aquatic TJrodeles, but here the 

 cylinders are wanting. 



