STUDIES ON THE 'TURBELLARIA. 459 
axis directed obliquely outwards and backwards. It is 
covered with a thin investing layer containing a few widely 
sundered nuclei. ‘Towards the inner end (base) one or more 
of these nuclei may be observed sunk below the level of the 
investing layer. The inner end of the ovary contains numerous 
nuclei intermediate in character between those of the invest- 
ing layer and those of the more mature ova. That the cells 
of the investing layer actually become converted into ova in 
the mature animal there is not sufficient evidence to establish 
definitely. 
With the exception of its inner end the ovary consists 
throughout of ova which extend right through the organ 
from side to side. 
Close to the ovary, and somewhat posterior as well as 
external to it, is the receptaculum seminis. It has a wall 
composed of a small number of cells with homogeneous 
protoplasm, usually not clearly distinguishable from one 
another. Internally this wall gives off irregularly arranged 
processes, which, though not forming actual partitions, give 
the outer part of the cavity a cellular character. In the 
interior is always a mass of spermatozoa. 
The oviduct, continuous with the receptaculum seminis, and 
opening towards the ovary, with the investment of which its 
outer layers are continuous, runs backwards, and then curves 
inwards to open into the atrium. Its muscular layers, thin 
in front, become greatly increased in thickness posteriorly. 
On the same side of the atrium as the oviduct (i. e. the right) 
opens a sac which appears, in position at least, to represent 
the bursa copulatrix. It is an oval sac, of small size, with 
thinnish wall, devoid of chitinous parts, which opens by a 
narrow neck or duct into the atrium. 
The atrium does not open directly on the exterior, but leads 
into a rounded chamber which acts as a uterus, and from this 
the common genital aperture leads outwards. The uterus is 
thus, as in most Proboscida and others (von Graff, 14, p. 139), 
merely the outer part of the atrium. In the uterus an egg, 
fully or partly completed, was very frequently found. Into 
