I0T4- Boycott. — Ayiatomy of Vitrina. 207 
(v.d. ') which crosses to the other side of the atrium, and 
opens into organ Y, which is to be regarded as the penis 
(Y) surmounted by a flagelhim (Y'). 
These two accounts are hardly compatible with one 
another, and the points at issue appeared to be worth 
further investigation. This I have been able to undertake 
through the great kindness of Mr. P. H. Grierson, who 
made a special expedition to Collon on my behalf, and of 
Mr. A. W. St elf ox, who placed at my disposal a number 
of specimens preserved in alcohol. 
At first sight it was difficult to understand how two 
such different anatomical descriptions could have been 
derived from the dissection of the same species, and it 
seemed probable that the material dealt with by Bowell 
must have been essentially dissimilar to that examined 
by Simroth. Actual dissection, however, soon showed 
the origin of both descriptions. I was unable, with needles 
and a dissecting lens, to definitely trace the vas deferens 
beyond the neighbourhood of the angle between the proximal 
ends of the free oviduct and X, and on the surface no 
continuation of the vas deferens towards Y could be found. 
Thus far the appearances were those described by Simroth- 
Taylor. On opening up the upper end of the atrium 
however, a stout white band was seen running from near 
the apparent termination of the vas deferens towards Y 
along the inner wall of, and projecting into, the atrium. 
This band was thickest at its origin, and tapered off gradually 
as it approached Y, and I was indeed unable to satisfy 
myself that it made a definite connection with Y. The 
appearances, however, were certainly not incompatible with 
Bowell's description. 
Any fuller interpretation being beyond the range of gross 
dissection, a complete series of microscopical sections was 
cut in paraffin from the lower part of the atrium to a point 
well above the tip of Y and the spermatheca. A study 
of these sections has I think shown what the facts really are : 
they are represented in a highly diagrammatic form in 
figure 4. The vas deferens passes downward to the base 
of X, where it becomes deeply imbedded in the wall of 
