BREEDING HABITS. The eggs may be fertilized internally or externally, just as they are being deposited in the water. In most eases they are left to chance, but in some species are carried in strands, or otherwise eared for by the male or female. A few have brood-pouches, and one toad rears its young in pits in the skin of the back. A few forms bring forth their young in an active condition. The gill-bearing or larval stage (axolotl) of Amblystoma tigrinum is capable of breeding, and under certain conditions may un dergo its metamorphoses. (See AXOLOTL.) The eggs are pigmented and usually undergo total and unequal segmentation. They possess a large amount of yolk, so much in a few eases, such as pipa, that the embryo lies coiled over the egg as though it were a fish. The blastula and gastrula stages are present, but are modified in form and manner of development by the pres ence of the yolk; the medullary groove develops by a pair oi upfoldings along the middle of the back, and by fusion of head and body, the tail becomes marked off; on the neck are two or three pairs of external gills. At about this time the tadpoles hatch, and begin to swim about or adhere to weeds by means of the sucker on the ventral surface of the head. At first the tadpole
has no mouth, but soon one develops, the external gills dwindle and are replaced by the internal, which are covered by a fold of skin. The hind limbs are the first to appear externally, lungs develop, and the larva can breathe both on land and in water. The gills of the Anura continue to dwindle and likewise the tail is gradually and completely absorbed. Tadpoles as well as some adult amphibia have the power of reproducing lost parts. See TOAD.
The early stages of amphibians are not al ways passed in water. Sonic of the European salamanders are viviparous, the young being born all developed, but still requiring water. The young of the viviparous Cleciliida% however, take to a terrestrial life as soon as they are born. So, too, certain frogs (e.g. Rana opisthodon, of the Solomon Islands) hatch from eggs laid out of the water as perfect, air-breathing frogs. In many species, as in the persistent gilled Crodela, the adult lives chiefly in the water; in other eases, as in the other Urodela, the Cieciliidx, and the Allure, the adult lives on find.