156 



DEVELOPMENT OF THE TADPOLE. 



We now come to the best known of all the batrachians, the Common Frog. 



The general form and api:)earance of this creature are too well known to need much 

 description. It is found plentifully in all parts of Europe and America, wandering to consid- 

 erable distances from water, and sometimes getting into pits, cellars, and similar localities, 

 where it lives for years without ever seeing water. The food of the adult Vrog 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 they 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 tlie 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 regulai'ly dotted with black spots, which lie in the shallows of a 

 river or the ordinary ditches that intersect the fields. Each of these little black spots is the 

 egg of a Frog, and is surrounded with a globular gelatinous envelope about a quarter of an 

 inch in diameter. According to gipsy lore, rheumatism may be cured by plunging into a 

 bath filled with Frog spawn. 



On comparing these huge masses with the dimensions of the parent Frog, the observer 

 is disposed to think that so bulky a substance must be the aggregated work of a host of 

 Frogs. Such, however, is not the case, although the mass of spawn is forty or fifty times 



DEVELOPMENT OF THE EGG AND OF THE TADPOLE OP THE GREEN FROG.— 1. Eggs just laid. 



8. The same, a short while later. 3. Tadpole in the Egg, 4 and 5. Tadpoles just out of Egg. 



6 to 12. Further development of the Tadpole, up to its last transformation. 



larger than the creature which laid it. The process is as follows : The eggs are always laid 

 under water, and when first deposited, are covered with a very slight but firm membranous 

 envelope, so as to take up very little space. No sooner, however, are they left to develop, than 

 the envelope begins to absorb water with astonishing rapidity, and in a short time the eggs are 

 inclosed in the centre of their jelly-like globes, and thus kept well apart from each other. 



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 appai-ent. In this state it is a black grub-like 

 creature, with a large head and a fiattened 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 appendages on each side of the head. The tadpole, with 

 the fully developed branchiae, is shown at Fig. 6, on the accompanying illustration. No sooner, 

 however, have these organs attained their size than they begin again to diminish, the shape of 



