LIFE-HISTORY OF THE COMMON GRASS-FROG 

 (Rana temporarid) 



This common Amphibian is an admirable illustration of evolu- 

 tionary principles, for it begins its existence as a fish-like tadpole, 

 which breathes by gills and feeds on vegetable matter, and later 

 on is gradually transformed into a limb-bearing, lung-breathing, 

 carnivorous frog, adapted to a life on land. Spawning takes place 

 in spring, each egg being enclosed in a gelatinous sphere, which 

 buoys it up, prevents overcrowding, and serves as a protection. 

 The just-hatched tadpole is mouthless and tailless, and for a time 

 holds on to a water-weed by means of adhesive discs on the under 

 side of its head. It quickly grows a broad swimming- tail, and 

 develops a mouth. Later on the limbs sprout out, and the bag- 

 like lungs grow from the under side of the gullet. Ultimately the 

 gills disappear, the gill-slits close, and the tail shrivels up. The 

 life-history of the individual Frog gives us some idea of the evolu- 

 tionary changes which have taken place in the past history of the 

 groups of Reptiles, Birds, and Mammals, the remote ancestors of 

 which were aquatic, fish-like creatures. 



