PHYLUM CHORDATA 



311 



many eggs are developed, only two larvse 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 



Fig. 958.— Ichtbyopllis glutinosa, xl. 1, a nearly ripo embryo, with gills, tail-flu, and 

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

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

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

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



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 in water, it swims about 

 like an ordinary aquatic larva, losing its long gills and developing 

 a new and shorter set. Most Gymnophiona 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 larvas of 

 most Gymnophiona have long external gills (Fig. 958). 



A very interesting case of pcedogenesis is furnished by the 

 Axolotl {Amhlystoma tigrinum). This animal frequently under- 

 goes no metamorphosis, but breeds in the gilled or larval state 



Flo. 959.— Amblystoma tigrinum. Larval or Axolotl stage? (From Mivajt.) 



(Fig. 959). But under certain circumstances the gills are lost, the 

 gill-slits close, and a terrestrial salamandrine form is assumed. It 

 is to the branchiate stage that the name Axolotl properly applies ; 



u 2 



