XXI] DEVELOPMENT 541 



Amphibia, passes the winter buried in the mud at the bottom 

 of ponds and takes no food. The conversion of some of the possible 

 eggs into fat to feed the rest is simply an example of the same 

 principle as the sacrifice of some of the dogs in an Arctic ex- 

 pedition to feed the rest. 



The development of Molge is interesting. The male emits 



the spermatozoa in a bundle which the female then 



introduces into her cloaca, and the eggs commence 



their development in the body of the mother. Soon afterwards they 



are laid and attached to water plants. After some time larvae are 



hatched out which in many respects resemble fishes. They are 



provided with three long feathery appendages on each side of the 



neck, in which there is a rich blood supply and active circulation. 



These are the external gills found only in Amphibia, Dipnoi and in 



FIG. 266. Larva of Triton, Molge cristata x 5. Showing external gills. 

 After Eusconi. 



Polypterus. There are also a pair of curious rod-like organs in front 

 of the gills attached to the sides of the head. These "balancers," 

 as they are termed, are possibly a first pair of external gills peculiarly 

 modified. They have mucous cells at the tip, and by means of 

 them the young larva suspends itself for hours at a time to plants. 

 There is a long fish-like tail, the organ of locomotion, with a fringed 

 fin. The fore-limbs are tiny buds. No trace of hind-limbs exists 

 and the gill-slits are not open. 



As development proceeds the fore-limbs make their appearance 

 provided with only two toes. The gill-clefts, three in number, 

 appear on each side. After a considerable time the third finger 

 appears and the hind legs sprout out as buds ; still later the fore- 

 limbs get all four fingers and the hind-limbs five. The animal has 

 now attained the appearance of the adult except in so far as the 

 gills are concerned. These are retained for a long time, and excep- 

 tionally, in Switzerland in high Alpine localities, the larva may 

 become sexually ripe and never leave the water. More usually with 



