558 



AMPHIBIA. 



MMM 



of moisture. The transformation may indeed lake place in water, and 

 both Axolotl and Amblystoma have been observed in the same lake. 

 Further, the absence or presence of gills is not the only difference 

 between the two forms. 



Amphibians are very defenceless, but their colours often conceal 

 them. Not a few have considerable power of colour-change. The 

 secretion of the skin is often nauseous, and therefore protective. 



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 fasting, 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 fer- 

 tilised ovum sinks into a little pocket, which is closed by a gelatinous 

 lid. In these pockets the embryos develop, perhaps absorbing 

 some nutritive material from the skin. They are hatched as 

 miniature adults. In Nototrema and Opisthodelphis the female has a 

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

 hatched. In Rhinoderma darwinii the male carries the ova in his 

 capacious croaking-sacs. In the case of the obstetric toad {Alytes 

 obstetricans), not uncommon in some parts of the Continent, the male 

 carries the strings of ova on his back and about his hind legs, buries 

 himself in damp earth until the development of the embryos is ap- 

 proaching completion, then plunges into a pool, where he is freed 

 from his living burden. Thus among Amphibians, as among Fishes, 

 the males sometimes take upon themselves the task of hatching the 

 eggs. 



In the Anura the ova are fertilised by the male as they leave the 

 oviduct ; in the newt the male deposits a spermalophore in the water 

 close to the female ; in Salamandra atra, S. maculosa, and Cecilia com- 



Fig. 240. — Caecilian [Ichthyophis) 

 with eggs. — After Sarasin. 



