292 KANSAS UNIVERSITY SCIENCE BULLETIN. 



h. Development of the Oocytes. 



The spots along the ovarian lining at which a conversioQ 

 from epithelial into germ cells is taking place can easily be 

 distinguished. At such points there is a great thickening of 

 the lining, or, we might say, a great multiplication of epithe- 

 lial cells has taken place, until the new cells project far out 

 into the lumen of the tube (PL XII, fig. 1, c, d, e) , sometimes 

 even filling the opening and crowding against the opposite 

 wall. These cells, at their earliest stage, do not differ in ap- 

 pearance from the epithelial cells around them, unless it be 

 in the nucleus, which seems to be slightly larger and richer 

 in chromatin. The form of both, however, is much the 

 same. Soon the nucleus increases in size until it almost 

 fills the cell, the cytoplasm growing some, though not in pro- 

 portion to the germinal vesicle. Out of the indefinite masses 

 of chromatin a slender spireme is formed, which seems to con- 

 sist of many long threads, crossing and winding among one 

 another. At what appears to be the extremity of each thread 

 is an enlargement which stains very densely. A close exami- 

 nation of these threads shows them to be made up of small seg- 

 ments, placed end to end. (.Figs. 4, 5, 6, pi. XII.) 



The stages between the spireme and the early oocyte were 

 clearly seen in ovaries fixed in Merkel's fluid, though much 

 material collected was lacking entirely in cells at this stage. 

 Lying embedded in the epithelial lining could be found divi- 

 sion figures at all stages. (PL XII, fig. 2.) The chromosomes 

 were distinct, but much crowded, so that, while I counted nine- 

 teen, I am by no means sure this is the actual number. The 

 cells grow rapidly from this period, and their development is 

 easily traced. They are always distinguishable by their clear 

 appearance ; large nuclei, with scattered patches of dimly 

 stained chromatin, and cytoplasm, thin and lacking in reticular 

 structure. (Fig. 7, pi. XII.) 



Though in the early oogonial stages the developing germ- 

 cells keep even pace, in their later development one gains de- 

 cided advantage and grows much more rapidly than the others. 

 We seldom find a group of oocytes equally developed, but 

 much more often we see one far advanced lying among many 

 oogonia, probably in the spireme stage. It seems that nat- 

 ural selection has come into play, choosing one from the many 



