The Common Leopard Frog 



twelfth day the gills are entirely covered, except the very tip ends 

 of two or three branches on the left side. (Fig. 211, April 20th.) 



For two or three days from this time there is little visible 

 change. The tadpoles (as black as toad tadpoles at the same 

 age) remain clinging to convenient supports by the suckers, now 

 greatly reduced in size. They sometimes start out on aimless 

 circling trips, but, on the whole, are not very active. The body 

 is now increasing greatly in diameter. This increase in diameter 

 is due partly to the development of special organs within. Through 

 the skin of the under side of the body can be seen the intestine, 

 spirally coiled like a watch-spring. This increase is due also to 

 the fold which covered the gills growing much farther back on 

 the body. Here it has united with the body wall on sides and 

 front, except for a small space on the left, where the tips of the 

 gills were last visible. It remains unattached at this point all 

 during the tadpole life. Thus is formed a spout for the exit of 

 water (Fig. 211, April 24th) from the internal gills, which replace 

 the external gills that we saw covered.' 



When we look at the tadpoles on the morning of April 24th 

 (sixteen days after the eggs were laid), we realize that the mouths 

 are open. Hungry tadpoles are swimming rapidly, instead of 

 aimlessly as before, and are nibbling the delicate ends of water- 

 weeds or vigorously scraping the green slime from the stones and 

 sticks at the bottom. ^ They are no longer jet-black, but are 

 made to look dark brown because of a fme mottling of gold spots 

 on the black. 



Their life for the next few weeks seems to have only four 

 needs: to swim rapidly, to eat almost constantly, to rest a little 

 sometimes, and to grow. Their enemies are many, and their ranks 

 are greatly thinned by them. It will be fortunate if they escape 

 the monstrous sucking jaws of the water-tiger.^ They glide up 

 to nibble the end of a green stem, and the stem comes to life and 

 sends out a powerful arm equipped with jaws that hold as in a 

 vice, while smaller jaws^ rapidly eat every part of the tadpole, ex- 

 cept, perhaps, the long coiled intestine. An unsuspecting tadpole 



' See BuUfrog, p. 236. 



- The mouth structure of the Leopard Frog tadpole corresponds with that of the Bullfrog tad- 

 pole. (See footnote, p. 235.) 



2 The water-tigers are larvoe of the diving-beetles (Dytiscidx). 

 ■•The larva of a dragon-fly (Libellulida?), 



181 



