342 AMPHIBIA xn. 22- 



Most of the amphibia have failed to effect the complete transfer to 

 land life : they return each year to the water to breed. Special modifica- 

 tions of the reproductive system for land life are therefore not found. 

 Secondary sexual differences are marked in many species. In frogs 

 the males precede the females to the water and then attract the latter 

 by their vocal apparatus. The male clings to the back of the female 

 by means of a 'nuptial pad', developed as an extra digit, prepollex, 

 on the hand (p. 317). Injection of male hormones or implantation 

 of testis will cause this organ to develop in young female frogs. 



In newts fertilization is ensured by an elaborate courtship. Sperms 

 are made into spermatophores by special pelvic and cloacal glands 

 and there are also abdominal glands, which produce a secretion attrac- 

 tive to the female. After a courtship ceremony the spermatophores are 

 picked up by the cloaca of the female and stored in a spermathecal 

 chamber. 



23. Digestive system of Amphibia 



Nearly all adult amphibia feed on invertebrates, mainly insects, 

 partly also worms, slugs and snails, spiders and millipedes. The larval 

 stages are usually omnivorous, but they may be cannibalistic, feeding 

 on the tadpoles of the same or other species — an interesting form of 

 provision for the next generation by excess productivity of the 

 mother. There are only minor modifications of particular species in 

 relation to their diet; as regards their food amphibia occupy a general- 

 ized or 'easy' habitat. The fact that they are not particular in choice 

 of diet has no doubt been part of the secret of their success. 



The tongue is the characteristic organ for catching the food and is 

 one of the special features required for terrestrial life, being reduced 

 in aquatic amphibia. In Rana it is attached to the floor of the mouth 

 anteriorly and flicked outwards by its muscles. To keep it moist and 

 sticky a special inter-maxillary gland is found. From the shape of the 

 premaxillae it can be deduced that this gland was present in labyrin- 

 thodonts. The saliva contains a weak amylase and some protease. It 

 is suggested that these serve to release sufficient substances for tasting. 

 Special tracts of cilia carry the secretion from the intermaxillary 

 glands to the vomero-nasal organ and palatal taste-buds (Francis, 

 1 961). 



Another feature made necessary by terrestrial life is the presence of 

 cilia to keep the fluids moving over the oral surfaces. These cilia are 

 absent in aquatic amphibia. 



The teeth on the premaxillae, maxillae, and vomers are used only 



