AI4 WILD ANIMALS 
The young are provided with gills with which they absorb sufficient 
air for the support of life from the water in which they live. In time 
they gradually lose these gills and develop lungs for breathing atmos- 
pheric air. This marks the transition from the larva to the adult. The 
latter, though generally quite at home in water as well as on land, must 
come to the surface of the water to breathe, and will drown if forced 
to remain submerged. The 
transformation from water-liv- 
ing to land-living animals is 
very interesting and may be 
compared to that which insects 
undergo in changing from the 
larva to the pupa and then to 
the adult. We describe here 
our three commonest families 
of amphibians. 
Frogs. — The life history of 
frogs shows a wonderful mode 
of animal development and is 
a favorite and instructive sub- 
ject for observation and study. 
The eggs are laid in masses 
in water, usually attached to 
Cyst weeds, where they hatch out 
THE DEVELOPMENT OF A Froc as tadpoles or polliwogs, con- 
I, eggs; 2, tadpole; 3, tadpole develop- sisting mainly of a large head 
ing hind legs; 4, same tadpole but larger; and a long tail. The gradual 
5, front legs appearing; 6, tail being ab- transformation of these tad- 
sorbed; 7, frog in adult form. z 2 
poles into frogs can easily be 
observed by putting some frog’s eggs into a glass jar in the school- 
room. Frogs also form an interesting example of hibernation. At the 
approach of winter they dive into the mud at the bottom of some 
body of shallow water and remain there in deep sleep till spring 
awakens them. 
There are in all several hundred species of frogs, the most famous 
being the common Leopard Frog and the Bullfrog. The latter species 
we do not see in the Northwest, and we shall concern ourselves only 
with the former. Its body color is green or greenish brown, and this 
