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. Ina 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 liye 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 (Pifa 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 Mototrema the female has a dorsal pouch of skin 
opening posteriorly, and within this tadpoles are hatched. In Rhzvo- 
derma darwinzi 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 cloace, 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 \aid on or under leaves in moist places. 
