DEVELOPMENT OF PARAVORTEX GEMELLIPARA 47l 



of fiat cells (fig. 51). A comparison of text figure 1 with Hallez's 

 brings out the difference between the two species as regards the 

 shape of the atrium, atrial canal and antrum femininum. In 

 P. cardii the atrium rises only a very little above the opening 

 into the atrial canal, while in P. gemellipara the antrum opens 

 into the atrium at the middle of its posterior surface. It was 

 stated in the introduction that the lack of a bursa semuialis 

 distinguishes the genus Para vortex from GraffiUa. 



The delicate- walled antrum femininum (text figs. 1, 2) ex- 

 tends from the atrium commune posteriorly and dorsally to 

 a point beneath the intestine. Strong sphincter muscle fibers 

 constrict the opening between antrum and atrium. So delicate 

 are the walls that only occasionally can the cells be made out. 

 Figure 4, referred to above, was drawn from a horizontally 

 sectioned animal which showed the walls of the antrum ex- 

 ceptionally well. The section chosen included only the upper 

 end of the antrum; the rest of the structure must be conceived 

 as lying below the plane of the paper. No marked bifurcation 

 is evident here on account of a distention with yolk cells; the 

 ends of the vitellaria border the whole posterior surface of the 

 antrum, while the terminal egg in each ovary presses inward 

 against its outer angle. No uterus homologous to that found 

 in many Turbellaria is present in Paravortex. In this regard 

 the following extract from von Bohmig's contribution to Bronn's 

 Klassen und Ordnungen des Thier-Reichs is of interest: 



''Bei alien diesen, dient, wie u. a. schon Bohmig fiir GraffiUa 

 muricicola und Vedjovsky flir Phaenocora hervorgehoben haben, 

 das Atrium commune oder Antrum femininum als Uterus . 

 zugeschrieben werden . ' ' 



Beneath the antrum and posterior to it are groups of single- 

 celled shell glands. Each contains a prominent nucleus and a 

 considerable amount of granular cytoplasm (figs. 3, 9), Al- 

 though it is difficult to determine the exact point at which these 

 glands are attached to the reproductive tract, they all converge 

 toward the lower end of the antrum near its union with the 

 atrium. As noted above, this character helps to distinguish 



