5 o ANIMAL LIFE 



to meet the needs of terrestrial movement have been 

 brought about from fish. Throughout the Amphibia, 

 with a few interesting exceptions, two pairs of limbs 

 corresponding to the paired fins of fishes serve in 

 various ways. In the newts the body is still fishlike, 

 but the limbs have acquired that division into upper, 

 middle, and lower segments (arm, forearm, and hand, 

 thigh, shank, and foot), that is so strikingly a character 

 of all the higher vertebrates. 



The movements of these animals and their rela- 

 tives, the salamanders, are exceedingly slow. The legs 

 are short and bent good, therefore, neither for bearing 

 weight nor as levers ; and the only powerful stroke 

 is the fishlike, lateral bending performed by the 

 tail under water. Frogs and toads, however, show 

 an advance in their locomotive powers by the leaping 

 and thrusting power of their long bent hind limbs. 



In the reptiles the powerful longitudinal muscles 

 of the back and tail, so characteristic of fish, are still 

 employed, and serve to assist the feet, which are short, 

 bent, and flattened. The movements of these animals 

 consist of short, violent rushes from point to point. 

 For sustained, rapid action neither the limbs nor the 

 disposition of the weight is suitable ; and reptilian life 

 enjoys extreme speed for short periods, alternating with 

 immobility for long ones. Their degeneracy is shown 

 in the disuse of limbs, a distinctively fishlike character, 

 which we find in snakes and many lizards. As com- 

 pensation for this loss the scales of the belly become 

 enlarged, and into them are inserted the ends of the 



