286 N. M. Stevens. 



lining of the body wall. Just below the oogonia, a group of cells 

 (Fig. 7) with a small lumen was found ; this is evidently the begin- 

 ning of the antrum, of which the oviduct is a cephalad continua- 

 tion. The section below shows a strand of cells running from the 

 body wall to the transverse membrane which separates the two 

 body cavities. Figs. 8 to 11 were taken from a somewhat older 

 ovary containing 35 to 40 oogonia. Fig. 8 is the most posterior 

 section of the ovary proper, showing a single oogonium surrounded 

 by cells which will later give rise to the antrum and ducts. The 

 section below (Fig. 9) shows more of the antrvim cells in the form 

 of a fold or outgrowth of the inner or mesodermal layer of the body 

 wall. (Cell outlines were not distinct.) The next section below 

 contained the remainder of these cells, a thin strand extending 

 to the transverse membrane. Fig. 10, the third section above 

 Fig. 8 and Fig. 11, the tenth above Fig. 10, show nothing more 

 than Figs. 5 and 6; i.e., no ducts yet formed. If, however, we take 

 a considerably later stage where the growing oocytes ,can be 

 distinguished from the oogonia (Fig. 12), we find in addition to 

 the endothelial membrane, two other layers of cells between the 

 body wall and the germ cells. These layers extend around the 

 sides of the ovary forming a 2-layered crescent (od). There is as 

 yet no lumen and no sperm-duct. 



Fig. 13 shows the next stage, in which a different kind of tissue 

 (sd) has come in between the two layers of the lateral wings of 

 the future oviduct. This tissue evidently must either be prolif- 

 erated from the layers which surround it or be formed by migra- 

 tion from those layers, as there is no other possible source. No 

 cell outlines can be distinguished, the tissue appearing to be a 

 syncitium of a fibrous nature with scattered nuclei. In this stage 

 mitosis is frequent in the oviduct walls, but rare in the new tissue 

 between them. Fig. 14 is a somewhat older ovary where the ovi- 

 duct walls are completely separated in the middle by the meeting 

 of the new tissue, which first appeared in the wings. In Fig. 

 15 we have a section of the lower or caudad end of the ovary, 

 showing the oviduct walls continuous with the as yet closed 

 antrum.. The reproductive pore is formed, but the cells have not 

 separated to form the antrum chamber and external opening. 



