296 



CLASS AMPHIBIA. 



Males and females are often distinguished by their size and 

 colour, and also by other peculiarities (vocal sacs, dorsal crests, 

 etc.) which are specially prominent at the breeding season. In 

 spite of the absence of organs of copulation, sexual intercourse 

 takes place, but it usually consists merely of an external 

 approximation of the two sexes {Anura in which the male em- 

 braces the female from the back), and results in the fertilisation 

 of the eggs outside the body of the mother. In cases in which the 

 spermatozoa are introduced into the female generative tracts, 

 spermatophores are formed, probably by the cloacal glands, 

 and introduced into the female cloaca by the application of the 

 swollen lip of the male cloaca to the anus of the female (Sala- 



mandrines). In such cases the eggs may 

 undergo their development within the 

 oviduct, and the young be born at a 

 more or less advanced stage of devel- 

 opment {Salamandra maculosa, S. atra, 

 Spderpes fuscus, etc.). It is only excep- 

 tionally that the parents have an instinct 

 to watch over the further fate of their 

 brood, as for example in Alytes (Fig. 168) 

 and the Surinam toad {Pipa dorsigera). 

 The male of Alytes winds the strings of 

 eggs round its hind legs and burrows into 

 the damp earth, and only gets rid of its 

 load when the embryonic development is 

 completed. In Pipa the eggs are placed on the back of the female, 

 which then develops a cell-like pouch round each egg. In this 

 case the whole development takes place in the egg. In Noto- 

 trema the eggs are conveyed into a spacious brood pouch beneath 

 the dorsal integument, in which the eggs undergo their embryonic 

 or their whole development. In Rhinoderma the eggs are placed 

 in the enlarged vocal sacs of the male, where they undergo the 

 whole of their development. In these cases the eggs are large 

 so that the young can undergo the whole or part of their later 

 development in the egg. This is the case also in some forms in 

 which the eggs are deposited in damp situations and the young 

 are not hatched until after the loss of the gills {Arihroleptis 

 seychellensis, Rana opisthodon, Hylodes martinicensis, etc.). 

 When the eggs are relatively small, they are usually laid in 



i"iG. 168. — Alytes ohstetrkans. 

 Male, with the string of 

 eggs (from Claus). 



