THE ANIMAL CLIMAX-THE CHORDATES 



301 





Fig. 13-27. A woodland pond with egg masses of the woodfrog (Rana sylvatica). 



times, and so on, producing furrows along 

 one side, then elongating, and finally devel- 

 oping a small tail. Sometime later a tiny 

 tadpole emerges from the jelly mass. By 

 means of a pair of suckers under the mouth, 

 the tadpole remains attached to the mass 

 for a few hours while it is undergoing fur- 

 ther development. Presently, however, it 

 begins to swim about and can be seen 

 to feed by a scraping movement of its 

 mouth as it moves along a leaf of a water 

 plant. In this stage it breathes by means of 

 gills just as fish do and as its ancestors did. 

 It is a vegetarian, feeding exclusively on 

 algae and other plant life. 



After some months or years, depending 

 on the species of frog, the tadpole rather 

 suddenly begins to develop miniature hind 

 legs while its tail becomes shorter. At the 

 same time its mouth grows larger and wider, 



and its digestive tract shortens. It gradually 

 seeks shallower water and occasionally 

 comes to the surface for air as its lungs de- 

 velop. These trips for air become more 

 frequent until finally the frog hops away 

 from the water, sans tail and strictly 

 carnivorous, a common sight to everyone. 

 Thus, in a brief period it has reenacted the 

 entire race history of this long and arduous 

 migration out of the water onto land, a most 

 remarkable feat! 



The summer months are spent in search 

 of food which consists of insects, spiders, 

 earthworms and even tadpoles and other 

 smaller frogs. These are sought in damp 

 places, usually near the water, although 

 some species such as the leopard frog ven- 

 ture considerable distances from the water 

 in search of food. Eggs develop rapidly 

 within the ovaries of the female, so that by 



