TADPOLES AND FROGS. 181 
(Eustachian tube.) Cut open the membrane covering 
the ear and use a probe. 
Using a prepared specimen showing the internal 
ergans, do you find the peritoneum? the mesentery ? 
the stomach * the intestine? the liver? the heart ? 
Do you find the lungs? 
Is there a diaphragm separating the heart and lungs 
from the stomach, liver, and intestine ? 
Dorsal to the viscera in a freshly prepared specimen 
look for nerves branching out from the spinal cord. 
Do you find nerve-masses (ganglia) on these nerves on 
each side of the spinal column? Are these ganglia 
connected by a nerve running lengthwise? Call this 
the sympathetic system of nerves. 
In a prepared specimen notice the brain and spinal 
cord. Sketch the brain in outline. How does this 
sketch compare with the sketch you have made of the 
brain of the fish ? c 
In what ways does a frog resemble a fish? How 
dees the frog differ from the fish ? 
Summary of Drawings. (a) Outline of organs seen 
in the visceral cavity. 
(4) Sketch of ganglia of sympathetic system with 
connecting nerves. 
(c) Outline sketch of brain of frog. 
Activities. Both the structure and the activities of 
the frog interest us because they are so much like those 
of man himself. The frog has been much studied 
because of the remarkable changes in structure and 
habits which the animal undergoes after leaving the 
egg. 
Taking Food. The frog lives on insects, worms, 
and other small animals. As a rule frogs eat only dur- 
ing the summer months, remaining torpid without food 
in winter. The tongue of the frog is peculiarly adapted 
for catching insects. It is fastened to the lower jaw 
by its front end, and turns a somersault when shot out 
at a fly. The hinder end is covered with a sticky 
