THE FEMALE 



55 



is not readily apparent because it requires water before it reaches 

 its maximum thickness. Eggs sectioned within the oviduct show the 

 jelly as a transparent coating just outside the vitelline membrane. As 

 soon as the egg reaches the water, however, imbibition swells the 

 jelly until its thickness becomes greater than the diameter of the 



egg- 



The function of the jelly is to protect the egg against injury, against 

 ingestion by larger organisms, and from fungus and other infections. 

 Equally important, however, is the evidence that this jelly helps the 

 egg to retain its metabolically derived heat so that the jelly can be 

 said to act as an insulator against heat loss. Bernard and Batuschek 

 (1891) showed that the greater the wave length of light the less 

 heat passed through the jelly around the frog's egg, in comparison 

 with an equivalent amount of water and under similar conditions. 



Oviducal blood vessels ~*% 



Passage of eggs through the oviduct. The eggs of the frog are greatly distorted 

 as they pass down the oviduct toward the uterus. They accumulate albumen 

 around them, but, since they spiral down the duct, the albumen jelly is evenly 

 deposited and the eggs become spherical as the jelly swells when the eggs pass 

 from the uterus into the water. 



