340 



GENERAL ZOOLOGY 



If the adult condition has not been reached, the tadpole 

 continues its growth the following summer. The hind legs 

 appear and grow to be about an inch long, when the fore- 

 legs suddenly appear. The front legs are really formed as 

 early as the hind legs, but they are kept beneath the skin 





Fig. 175. Development of a frog 1 



A, eggs in water ; B to E, stages in the division of the egg and arrangement of 

 the cells to form the embryo ; F, recently hatched tadpoles clinging to water 

 plants ; G and H, full-grown tadpoles with hind legs developing ; I and J, trans- 

 formation of tadpole into adult form showing gradual loss of tail; K, fully 



formed frog 



for a while. The broad and compressed tail, which forms 

 the tadpole's chief organ of locomotion, is gradually ab- 

 sorbed, and the young frog finally hops out on land with 

 only a stump of a tail remaining. In the time these changes 

 have been taking place externally, important changes have 

 gone on inside : the gills have been replaced by lungs ; one 



1 Reprinted by permission from Textbook of General Zoology, by W. C. Curtis 

 and M. J. Guthrie, published by John Wiley & Sons, Inc. 



