43 
spiral ridge of its epithelium“, which is apparently developed for 
the purpose of retarding the passage of the eggs and perhaps at 
the same time cause their rotation, during which the shell giand 
substance would be applied. In Bergendalia this spiral ridge of the 
epithelial wall in the shell giand duet is even more pronounced. 
According to Laidlaw (1903), the vagina in B. anomala is „twisted 
into a remarkable spiral coil, making some five complete turns‘' 
and in B. diversa „twisted at a part of its course into a compact 
spiral coil of some five turns“ (Yeri and Kaburaki 1918). 
Pars interna vaginae has in Discostylochus an epithelium that is 
less ciliated but of a height similar to that of pars externa vaginae, 
and the muscular wall is also made up of fine fibres densely packed, 
The unpaired median uterine duet is directed upwards and slightly 
forwards and has, as in the case of the distal end of each uterus, 
a thicker and very compact circular muscular layer with a well- 
developed nuclear zone outside the muscularis. 
Ductus genito intestinalis forming the continuation of pars interna 
vaginae runs first backward and then curving along the vagina 
approaches the ventral musculature of the body. The cell plasma 
in the epithelial cells is very dense and giand cells are totally 
absent. After a sharp lateral turn the duet continues caudally, a 
little to the side of the median line, describing finally a sharp 
curve upwards, simultaneously making a lateral twist, and running 
to an intestinal coecum, which it enters on its ventral side (Plate II, 
Pigs. 4 and 5). The lateral twists are the cause of the faet that 
in the section photographed to show the entrance of the duet in 
the intestine only a part of the epithelial tube of the ductus g. i. 
is present. The muscular wall on the photograph shows, however, 
that it is the same duet, and the neighbouring sections demonstrate 
clearly the epithelial tube and a non-compressed lumen. 
Ductus genito-intestinalis has a well - developed epithelium, 
which is higher than that of the pars interna vaginae and has 
very thick ciliated epithelium (Plate II, Fig. 5). The muscular wall, 
as well as the epithelium, gradually inereases in thickness, and 
consists almost exelusively of coarse circular muscle fibres. The 
muscular envelope is surrounded by a zone of nuclei (Plate II, 
Fig. 4), although at the same time scattered nuclei are found in 
the muscle layer. Some of these belong to the dilator fibres. One 
