588 



AMPHIBIA. 



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Islands, live in regions where there are few pools. In such cases the 

 development is completed within the egg-case, and a lung-breathing 

 tailed larva is hatched in about fourteen days. 



In some Mexican and N. American lakes there is an interesting 

 amphibian known as Amblystonia or Siredon. It has two forms one 

 losing its gills (Amblystotna], the other retaining them (Axolotl). Both 

 these forms reproduce, and both may occur in the same lake. Formerly 

 they were referred to different genera. But the fact that some 

 Axolotls kept in the Jardin des Plantes in Paris lost their gills when 

 their surroundings were allowed to become less moist than usual, led 

 naturalists to recognise that the two forms were but different phases of 

 one species. It has been shown repeatedly that a gilled Axolotl 

 may be transformed into a form without gills ; and this metamorphosis 

 seems to occur constantly in one of the Rocky Mountain lakes. 

 Abundant food and moisture favour the persistence of the Axolotl stage. 

 Amphibians are very defenceless, but their colours often conceal 



them. Not a few have consider- 

 able power of colour-change. 

 The secretion of the skin is often 

 nauseous, and therefore pro- 

 tective. 



Many Amphibians live alone, 

 but they usually congregate at 

 the breeding seasons, when the 

 amorous males often croak noisily. 

 Alike in their love and their 

 hunger, they are most active in 

 the twilight. 



Their food usually consists of 

 worms, insects, slugs, and other 

 small animals, but some of the 

 larval forms are for a time 

 vegetarian in diet. They are 

 able to survive prolonged fast- 

 ing, and many hibernate in the mud. Though the familiar tales of 

 " toads within stones " are for the most part inaccurate, there is no 

 doubt that both frogs and toads can survive prolonged imprisonment. 

 Besides having great vital tenacity, Amphibians have considerable 

 power of repairing injuries to the tail or limbs. 



Although the life of Amphibians seems to have on an average a low 

 potential, even the most sluggish wake up in connection with re- 

 production. The males often differ from their mates in size and colour. 

 Some of their parental habits seem like strange experiments. 



Thus in the Surinam toad (Pipa americana] the large eggs are placed 

 by the male on the back of the female, and fertilised there. The skin 

 becomes much changed doubtless in response to the strange irritation 

 and each fertilised ovum sinks into a little pocket, which is closed by 

 a gelatinous lid. In these pockets the embryos develop, perhaps ab- 

 sorbing some nutritive material from the skin. They are hatched as 

 miniature adults. In Nototreina and Opisthodelphis the female has a 

 dorsal pouch of skin opening posteriorly, and within this tadpoles are 



FlG. 287. Cascilian (Ichthyophis] 

 with e??s. After Sarasin. 



