290 KANSAS UNIVERSITY SCIENCE BULLETIN. 



Vr. OVARY. 



The ovaries of the spider are the most prominent organs of 

 the abdomen. They lie completely embedded in a soft brown 

 tissue, the so-called liver, more to the ventral than to the dor- 

 sal side of the body cavity. In the adult they extend from the 

 anterior end of the abdomen to the posterior wall. As the eggs 

 develop and increase in size, the ovary grows in thickness and 

 width, until the entire abdomen becomes much enlarged. The 

 liver grows proportionately thinner as this process continues. 

 By a careful incision of the dorsal integument, and laying back 

 the mass of liver, the numerous eggs may be seen. In Lycosa 

 they are a rich yellow and very large, while in Theridion they 

 are smaller and very white. 



The ovaries thus filled with eggs have much the appearance 

 of two bunches of grapes lying side by side. The entire mass 

 is very soft, as the eggs have at this time no firm covering, but 

 a most flexible and delicate membrane. Each ovary is con- 

 nected at its anterior end with an oviduct, the ovaries them- 

 selves communicating at no point. Figure 1, plate XII, 

 represents the posterior ends of two ovaries as they lie in the 

 body cavity. 



VII. OBSERVATIONS. 



a. Development of the Ovary. 



The reproductive organs of the spider differentiate at a very 

 early period from the body cells, appearing first as two folds 

 lying parallel to each other along the ventral aspect of the 

 abdominal cavity. These assume a more definite shape as the 

 animal grows, until there are soon two hollow cylindrical organs 

 replacing the folds. The cells composing the ovaries at this 

 early stage are apparently all alike, merely a mass of germinal 

 epithelium surrounding a very small lumen. The outer wall 

 consists of a layer of muscles, and between it and the epithelial 

 lining lies a thin structureless membrane, the peritoneal coat, 

 which cannot be distinguished until the follicles are formed. 



So far the outer wall has a smooth surface, but very soon a 

 change takes place on the interior of the tube which alters the 

 appearance of the entire ovary. This change is as follows : 



