408 
Cestode Genus Oochoristica 
part of its course to form a receptaculum seminis. Both vagina and vas 
deferens pass between the dorsal and ventral excretory vessels and dorsal to 
the lateral nerve. 
Remarks on the Uterus and the appearances observed in 
Gravid Segments. 
Beddard (1914 and 1916) has remarked upon the history of the uterus and 
the embedding of ova in the parenchyme in certain species of Oochoristica, and 
has suggested that the study of these points may prove to be of value in 
• deciding the difficult question of the relationships of this genus and Linstowia. 
1 have paid some attention to the phenomena in question in the present 
species, and propose to give a brief account of the facts as far as I have been 
able to follow them. 
The uterus (PI. XXI, fig. 3, TJt.) is at first an irregularly branching thin- 
walled sac lying on the ventral side of the segment, near the ventral limit of 
the medullary parenchyme. It is flattened dorso-ventrally so that for the 
most part it is not capable of holding more than two layers of eggs. At first 
the eggs in utero are similar in appearance to those still in the ovary, except 
that they are invested by a thin membrane. Segmentation, however, very 
soon begins, and proceeds rapidly in the uterus. The uterine wall is very 
delicate, consisting of a single layer of flattened cells, indicated by scattered 
nuclei. The uterus sends out finger-like diverticula, containing ova, laterally 
as far as the ventral excretory vessels, but not beyond them. It extends 
nearly as far as the transverse vessels at the back of the segment, but does 
not reach in a forward direction as far as the most anterior testes. 
The uterus only persists in this condition through a very limited number 
of segments—I am unable to state exactly how many. The next stage is one 
in which the ova previously contained in the uterus are seen to be scattered 
singly throughout the parenchyme. Each is now contained in a space lined 
by a layer of flattened cells, like those seen in the wall of the uterus. The 
spaces, in fact, may probably be regarded as nipped-off portions of the uterine 
cavity. 
Some of the ova (which by now contain well-advanced embryos) now 
penetrate laterally beyond the excretory vessels: they also penetrate dorsally, 
and many may be seen lying between the testes. They do not, in this species, 
appear to go beyond the limits of the medulla. (In 0. marmosae Beddard, 
they extend into the cortex—see Beddard, 1914.) Up to this stage, the embryo, 
within its parenchyme-space, is surrounded only by the thin membrane which 
was already present in the uterus. 
Finally, in the last few segments, the testes and most of the other organs 
disappear, and the ova lie in a kind of honeycomb-like structure into which 
the medullary parenchyme has been transformed, and which may perhaps be 
compared (with reservations, however) with the “paruterine organ '* met with 
in certain genera. The spaces in which the ova lie in the parenchyme appear 
