608 AMPHIBIA. 



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 considerable power of colour-change. The 

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

 cases, such as Ceratophrys dorsata, there is a bony shield on the back 

 made of a number of small pieces arising as ossifications of the inner 

 stratum of the dermis and of the subcutaneous connective tissue. It is 

 interesting to notice the occurrence of numerous hair-like filaments on the 

 sides and thighs of the males of a Kamerun frog (Astylosternus robustus}. 



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 

 fertilised internally and placed by the everted cloaca of the female upon 

 the back, the male apparently helping in the process. 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 Nototrema the female has a dorsal pouch of skin 

 opening posteriorly, and within this tadpoles are hatched. In Rhino- 

 derma 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 approaching completion, then plunges 

 into a pool, where he is freed from his living burden. 



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

 oviduct ; in most Urodela fertilisation is internal, sometimes by approxi- 

 mation of cloacte, sometimes by means of complex spermatophores 

 which the male deposits in the water close to the female. 



The eggs of the frog are laid in masses, each being surrounded by a 

 globe of jelly ; those of the toad are laid in long strings ; those of newts 

 are fixed singly to water-plants ; those of some tree-toads, such as 

 HylodeS) are laid on or under leaves in moist places. 



