558 AMPHIBIA. 



of moisture. The transformation may indeed take 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. 



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 repairriqg injuries to the tail 

 or limbs. ^ 



Although the life of Amphibians seems to have gatea ^ average a low 

 potential, even the most sluggish wake up in conn^ 'fi^ reproduc- 



tion. The males often differ from their meitesjru^bvtetis r % Some 

 of their parental habits seem like strange ^gxperimtof/'?'^?/ ;. ^ 



Thus in the Surinam toad {P/pa auiericana), th^a iiv '*' ^laced 

 by the male on the back of the female and fertili^^'J^^-*!. ne skin 

 becomes much changed — doubtless in response t^^ Lrange irritation 

 — and each fertilised ovum sinks into a little pocket, ^" nich is closed by 

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

 ing 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 

 hatched. In RhinoderDia 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 embr)-os is ap- 

 proaching completion, then plunges into a pool, wdiere 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 spermatophore in the water 

 close to the female ; in Salaniandra atra, S. maculosa, and Circilia 

 coinpressicauda the fertilisation must take place internally, for the young 

 are hatched within the mother. 



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 fi.xed singly to water plants ; those of some tree-toads, such 

 as Hylodes, are laid on or under leaves in moist places. 



In Salamaiidra atra, Pipa americana, Hylodes, and Cizcilia coin- 

 pressicauda, the young are hatched as miniature adults ; and marked 

 metamorphosis can hardly be said to occur in any Urodela. 



There are about 900 living species of Amphibia, most of them tail- 

 less. All are averse to salt-water, hence their absence from almost all 



