XIII 



PHYLUM CHORDATA 



301 



Toad (Pipa americana, Fig. 968) the skin on the back of the female 

 becomes soft and spongy during the breeding season : the eggs are 

 placed on it by the male, and each sinks into a little pouch of skin 



FIG. 969.-Iclitliyophis glutinosa, x 1. 1, a nearly ripe embryo, with gills, tail-tin, and 

 still with a considerable amount of yolk ; 2, female guarding her eggs, coiled up in a hole 

 underground ; 3, a bunch of newly-laid eggs ; 4, a single egg, enlarged, schematised to show 

 the twisted albuminous strings or chalazae within the outer membrane, which surrounds 

 the white of the egg. (After P. and F. Sarasin.) 



covered by a gelatinous film. The embryos, which have a large yolk- 

 sac, develop in these pouches ; they never possess external gills, and 

 are hatched in the adult form. In the case of several species the 

 tadpoles are carried about by the female, adhering to her dorsal 

 surface by suckers or by a viscid secretion. Another Anuran, 

 Pseudis paradoxa, is remarkable for the fact that the tadpole is 

 many times larger than the adult. 



Some Salamanders (S. maculosa and S. atra) and a species of 

 Caecilia are viviparous. In the Black Salamander (S. atra), though 

 many eggs are developed, only two larvae survive, one in each 

 oviduct, these being nourished in later stages by means of the 

 remainder of the eggs. The larva in this species possesses long 

 plume-like external gills during its existence in the oviduct, shedding 

 them before birth. 

 If, however, the 

 unborn young is 

 removed from the 

 oviduct and placed ^c: 



in water, it swims 

 about like an ordi- 

 nary aquatic larva, 

 losing its long gills 

 and developing a 

 new and shorter 

 set. Most Gym- 

 nophiona lay their eggs in burrows, but the larvae in some cases lead 

 an aquatic life for a time, and during this period possess, like tadpoles, 

 a tail with a tail-fin which afterwards undergoes absorption. The 

 larvae of most Gymnophiona have long externargills (Fig. 969). 



Fiu. 070. -Amblystoma tigrinum. Larval or Axolotl stage. 

 (From Mivart.) 



