XIII.] THE FROG. 255 



the tubule, which accordingly appears to be 

 lined by them. 



c. The spermatozoa (B. 10, a. 7). 



1. The ovary. 



The structure of this organ is easiest made out shortly 

 after the breeding time. Remove one of the ovaries, 

 place it in water, and make an incision into it : it will 

 be seen to contain a cavity, and projecting upon the 

 walls of this cavity and also upon the outer surface of 

 the ovary are numerous round eminences of various 

 sizes : these are ova in different stages of development, 

 and the large ones will be seen to have become more 

 or less pigmented. 



Tease out a bit of ovary in normal saline solution : 

 cover, and examine with a low power. 



a. Note the ova, many much smaller than those 

 which were seen (1) with the naked eye : they 

 appear as granular spherical masses with a clearer 

 central patch. 



I. Examine with a high power a portion of your 

 specimen containing some of the younger and 

 more transparent ova. Note 



a. The thin structureless membrane, vitelline mem- 

 brane, enveloping each. 



/5. The granular matter (yelk, mtellus) forming 

 most of the ovum. It sometimes appears to 

 be composed of an outer granular and an inner 

 clearer layer. 



