CLASS IV. BATRACHIA: ORDER 1. ANURA. 409 
more or less rapid according to the temperature ; the greater the heat the more speedy is the 
process. The annexed engraving illustrates the progress of the young animal. 
HATCHING AND PROGRESS OF THE YOUNG FROG. 
Figure 1 represents the embryo as it appears several days after the egg is deposited. Figure 
2 gives an outline of its form ; the arrows at the side of the head show the currents of water 
which are seen to flow to the branchiaj by the breathing of the young animal. A short period 
brings it to the form represented in Nos. 3 and 4, the latter representing the head. Figure 
5 shows the form of the tadpole when first hatched, which usually takes place about four weeks 
after the depositing of the egg. Figures 6, 7, 8, show various stages of its development ; the 
latter representing the tadpole, called polhjtoog by the boys of New England ; this for some time 
now undergoes little change of form, but increases in size. At length the hinder legs bud, and 
are gradually developed, as seen in No. 9 ; the fore-legs are ere long produced in a similar man- 
ner. The tail begins now to diminish, as seen in No. 10, and is finally absorbed into the body 
and disappears. The tadpole, which for a time was like a fish, and breathing by branchias or 
gills, and feeding on the vegetable food of fishes, is now a frog, breathes the air by true lungs, 
and betakes itself to the land, where it pursues the avocations of its new and higher life. 
Whereas it before swam by means of a tail, it now leaps, and as before it ate only roots and grass, 
it now becomes a hunter of insects and worms. This, or a very similar process of reproduction 
is common to all the species of this family. 
The common frog is said to be five years in attaining its full size, and its life is supposed to 
extend to twelve or fifteen years. It passes the winter in a state of torpidity, either in holes in 
the earth, or buried in the mud at the bottom of ponds, without the possibility of feeding or 
breathing. The voice of the frog is a pecuHar hoarse cry, weh known as croaking. In the males 
there is a large sac on each side of the neck, which is inflated with air during the croaking, and 
probably serves to increase the sound. 
The species of frogs are very numerous, and distributed very widely over the globe ; they are 
especially abundant in tropical countries. Their habits are generally very similar to those of 
the common frog. Notwithstanding the popular notion to the contrary, frogs are said by Bell 
to be found in Ireland, though they were probably introduced from England more than a century 
ago. Of the European species, the most celebrated is the Edible Froo, R. esculenta, which is 
exceedingly common in standing water on the continent, although in England it appears to be 
rare. It is rather larger than the common frog, and its nocturnal croakings are so loud and dis- 
agreeable, that temporary dwellers in the neighborhood of ponds frequented by it, are often pre- 
vented from sleeping by its clamorous chorus. It is this species that is most approved of on the 
continent for culinary purposes. It is very extensively used in France. 
Vol. II.— 52. 
