AMPHIBIA. 28l 



(most urodeles) or three somites (anura) or several segments 

 (gymnophiona, Amphiuma.} It is replaced later by the perma- 

 nent mesonephric kidney, the anterior end of which in the male 

 becomes subsidiary to reproductive purposes (p. 129). In the 

 gymnophiona it is markedly segmental. The ovaries are long 

 bands in the gymnophiona, elongate sacs in the urodeles, and 

 shorter sacs divided by transverse partitions in the anura. The 

 eggs, in their passage through the Miillerian ducts, become en- 

 veloped in a gelatine which swells in contact with the water. 

 The Miillerian duct always persists in the male. The sperm 

 passes through the anterior part of the kidney, and thence to 

 the exterior by the way of the urinary duct. In many urodeles 

 it becomes enclosed in packets (spermatophores). Connected 

 with the reproductive organs are branched ' fat bodies ' which 

 probably are connected with the nutrition of the reproductive 

 structures (p. 200). 



Fertilization by means of the spermatophores is internal in 

 urodeles, external in the anura. The eggs are laid in the water, 

 and left without further care by most forms. A few, however, 

 have interesting breeding habits. Thus Amphinma and Ichthy- 

 ophis wrap the cords of eggs around the body ; in Alytcs the 

 ( male wraps the cords around his legs. In RJiinodcrma there is 

 a large gular fold into which the eggs are received, while in 

 Nototrema and Notodclphys a brood pouch, open behind, is formed 

 by a duplication of the skin of the back. In the Surinam toad, 

 Pipa, the eggs are spread upon the back, the skin of which 

 thickens around each egg so that it assumes the character of 

 honeycomb, each cell being occupied by an egg which devel- 

 opes in this position until the adult characters are assumed. A 

 few species {Salamandra atra, S. macitlosa, Ccecilia compressi- 

 cauda) bring forth living young, while Amblystoma tigrinnm fre- 

 quently breeds in the larval or ' Siredon ' stage. 



The eggs contain a large amount of yolk, and undergo a 

 total but unequal segmentation (Fig. 214), the result being the 

 formation of a blastula with small cells on one side and larger 

 (entodermic) cells on the other, and an eccentric segmentation 

 cavity (Fig. 215). The gastrula arises in part as an inpushing, 

 in part as the result of an overgrowth of the ectoderm, and be- 



