THE COMMON FROG. 



519 



watir. The food of the adult frog is wholly of an animal character, 

 and consists of slugs, possibly worms, and insects of nearly every kind, 

 the wire worm being a favorite article of diet. A little colony of Frogs 

 is most useful in a garden, as its members will do more to keep down 

 the various insect vermin that injure the garden than can be achieved 

 by the constant labor of a human being. 



The chief interest of the Frog lies in the curious changes which it 

 undergoes before it attains its perfect condition. Every one is familiar 

 with the huge masses of transparent jelly-like substance, profusely and 

 regularly dotted with black spots, which lie in the shallows of a river 

 or the ordinary ditches that intersect the fields. Each of these little 

 l)lack spots is the egg of a Frog, and is surrounded with a globular 

 gr'latinous envelope about a quarter of an inch in diameter. 



In process of time certain various changes take place in the egg,'and 

 at the proper period the form of the young Frog begins to become ap- 

 parent. In this state it is a black grub-like 

 creature, with a large head and a flattened 

 tail. By degrees it gains strength, and at 

 last fairly breaks its way through the egg, 

 and is launched upon a world of dangers 

 under the various names of tadpole, pollywog, 

 toe-biter, or horsenail. 



As it is intended for the present to lead an 

 aquatic life, its breathing apparatus is formed 

 on the same principle as the gills of a fish, but 

 is visible externally, and when fully developed 

 consists of a double tuft of finger-like append- 

 ages on each side of the head. The tadpole, 

 with the fully-developed branchiae, is shown at Fig. a on the accompany- 

 ing illustration. No sooner, however, have these organs attained their 

 size than they begin again to diminish, the shape of the body and head 

 being at the same time much altered, as is seen in Fig. b. In a short 

 time they entirely disappear, being drawn into the cavity of the chest 

 and guarded externally by a kind of gill-cover. 



Other changes are taking place meanwhile. Just behind the head 

 two little projections appear through the skin, which soon develop into 

 legs, which, however, are not at all employed for progression, as the 

 tadpole wriggles its way through the water with that quick ilndulation 

 of the flat tail which is so familiar to us all. The creature then bears 

 the appearance represented in Fig. c. Presently another pair of legs 

 make their appearance in front, the tail is gradually absorbed into the 

 body — not falling off*, according to the popular belief — the branchiae 

 vanish, and the lungs are developed. Fig. d represents a young 

 Frog just before the tail is fully absorbed. 



Tadpoles. 



