90 
AMPHIBIANS 
have been preserved in formalin can be easily dissected. Examine the 
digestive organs: first the mouth, then the esophagus, stomach, small 
and large intestine, and cloaca. For convenience, the liver will have to 
be removed. The pancreas can be seen as a small whitish structure in 
the loop between the stomach and the intestine. The spleen is a round 
red organ usually found near the large intestine. 
A pair of narrow kidneys lies close to the back and is connected by 
ducts with the cloaca. The spermaries are found attached to each kid¬ 
ney near the front end and the sperm cells escape to the exterior by the 
kidney ducts. In the female frog the large ovaries occupy most of the 
Figure 75.—Frog Eggs. 
space of the body cavity. A pair of oviducts opens into the body cavity 
just back of the stomach. The eggs escape from the ovary into the body 
cavity. 
The nervous system is enclosed in bone that is easily removed from 
the dorsal surface. The brain should be studied and the following 
divisions recognized: cerebral hemispheres ending in front in the ol¬ 
factory lobes, which are not clearly marked. Just back of these the 
two large roundish optic lobes which are attached to the midbrain 
{thalamencephalon, thal-a-men-ceph'a-lon). The cerebellum is small, 
and the medulla passes into the spinal cord without any sharp dividing 
line. 
78. Development. — Late in March and early in April 
the frogs gather in ponds to lay their eggs. The eggs are 
surrounded by a jelly-like substance which holds them to¬ 
gether. As the eggs are being laid by the female frog, the 
male frog spreads a large number of sperm cells over the whole 
