128 PROCEEDINGS OF THE ACADEMY OF [Feb., 



doubtless owing to the presei\ce of small yolk granules. The nuclei 

 possess the general character of those of the tissue cells, being vesic- 

 ular, and containing a large chromatin nucleolus. 



The oocytes, or ovarian eggs, constitute the greater part of the 

 ovary, and form a closely packed mass entirely filling up the remainder 

 of the space below the intestine, which lies close to the dorsal body 

 wall. The oogonial mass is commonly crowded to one side of the 

 oocytes, thus lying laterad and often somewhat ventrad of the latter. 

 In some cases, indeed, a large oocyte, apparently full grown, is found 

 in the posterior portion of the ovarian chamber, caudad of the oogonia. 

 The mature female ova are in the neighborhood of 100 n in diameter, 

 closely approximating that of the body of the parent. The diameter 

 of the ova destined to form males is much smaller, i.e., about 30 fx. 



The first maturation division, as least as far as the metaphase, occurs 

 within the ovary, and has been observed by both Conklin (1906) and 

 myself. \o\\ ]\Ialsen (1906) states that in one instance only did he 

 find maturation spindles within the ovarian chamber. It is curious 

 to note that in those preparations which showed the karyokinetic 

 figures, all of the mature oocytes appear to be dividing simviltaneously 

 and at the same rate, since all of the spindles were in the same phase, 

 namely, the metaphase. The probable explanation of this phenom- 

 enon is that, as in Ophryotrocha (Korschelt, 1903), the oocytes 

 remain at this stage of division until penetrated by the sperm. All of 

 these dividing ova displayed a well-marked peri-vitelline layer, which 

 stains strongly in Meyer's mucicarmine. This layer, however, does 

 not extend completely around the ova, but is seen onl}^ on their free 

 surfaces, its formation being in some way prevented by contact with 

 other ova. 



The peritoneal investment of the ovary consists of an extremely 

 delicate epithelium which encloses the oogonia and oocytes as in a bag, 

 and is attached posteriorly to the apex of the pyriform oogonial mass 

 (see figs. 7 and 21, per.). From the outer surface of the peritoneum 

 thin strands of protoplasm are here and there given off to the neighbor- 

 ing alimentary canal and body w'all. The existence of this epithelial 

 covering w-as for a long time a matter of much doubt in my mind, and 

 it is only after careful study of sections of the best preserved material 

 that I have arrived at the conclusion stated above. In some cases the 

 peritoneum is wtII marked and easily demonstrated, as in fig. 7; in 

 others, as in the section represented by fig. 21, the peritoneum is ex- 

 ceedingly tenuous. That it is a true epithelial layer is shown by the 

 presence in it of small nuclei. Von Malsen (1906) also observed this 



