The Common Bullfrog 



perhaps during June and July, however, that most of the final 

 transformations are made. 



If we bring tadpoles from the pond in early July, we shall 

 find that many of them have hind legs. The size of the tadpole 

 is surprisingly large. It may measure six or seven inches from 

 the mouth to the end of the tail, the tail alone being three or four 

 inches long. Let us examine one of these tadpoles (Fig. 283) 

 closely to see how he is fitted to live his life in the water, sur- 

 rounded by innumerable enemies. If we take one into our hands, 

 we find it slippery and soft. The skeleton is cartilaginous. The 

 creature has no means of defence, but must depend wholly on 

 hiding and on flight. Fortunately, he is well provided for both. 

 The marbled speckled brown of his moist skin makes him almost 

 invisible on the muddy bottom, or among brown stems and leaves 

 in the pond. The long tail has a broad fin, and is provided with 

 strong muscles. With this equipment the tadpole can swim rap- 

 idly and vigorously, and can splash the mud of the bottom so as 

 to obscure his course, and make it possible for him to glide off 

 unseen in some new direction. The hind legs are fairly well de- 

 veloped, and the broad feet are webbed to the ends of the toes, 

 so they give effective help in swimming. The eyes are large and 

 conspicuous; in fact, they seem already to show a slight ele- 

 vation, as though they were beginning to take on the character- 

 istics of the frog's eyes. The mouth is small. It consists of 

 fleshy lips covered with rows of tiny teeth. 1 The lower lip is 

 especially broad and ruffled, and bears along its lower edge rows 

 of fleshy papilla, which, probably, serve for determining the 

 nature of substances when the tadpole is seeking food. Between 

 the lips, and somewhat within them, is a horny beak, which, 

 though very small, is much like a bird's beak in shape. It con- 

 sists of an upper and a lower jaw, strong, and very thin and sharp 

 at their edges. The mouth is well fitted to bite off the delicate 

 ends of leaves and stems, or to scrape off the tender green or 

 brown plants from sticks and stones. It is equally adapted for 

 eating animal food. The Bullfrog tadpole (like that of the Green 

 Frog and of the Wood Frog) is especially fond of any animal food 



1 The mouth structure of the bullfrog tadpole is as follows: The upper lip is relatively narrow, 

 and bears only one complete row of teeth; the lower lip is very broad, has three rows of teeth and 

 a border of papilla?; the border of the lower lip extends upward to the upper lip, and is doubled in 

 at the corners of the mouth. This structure corresponds almost exactly with that of the tadpoles 

 of three other water-frogs, R. pipiens, R. palustris, and R. damitans. 



235 



