342 A Lesson in Comparative Histology. [June, 
vestcule seminales, which open into the long ducts of the sperma- 
ries and end blindly. If one of these be isolated, and then colored 
with hzmatoxiline or carmine, and examined in a drop of glyc- 
erine with the microscope, its walls will exhibit a great many 
minute colored dots of oval shape; these are the so-called nuclei 
of the cells; it is evident that they form but a single layer, for in 
no part of the wall of the tube do they lie over one another. By 
looking carefully it is possible to distinguish a faint polygonal 
outline around-each nucleus; these outlines correspond to the 
surfaces by which the cells abut against one another. Thus we 
learn at once that a cell is a very minute body with granular 
contents, and a distinctly differentiated central portion, the nucleus, 
and moreover that the cells are laid close against one another, and 
cemented together by thin intervening layers known as the zu/er- . 
cellular substance. But every vesicula consists of a wider upper 
portion, which is usually found filled with spermatozoa in the 
mature animal, and the walls of which are composed almost 
entirely of the layer of cells just described; and a narrower por- 
tion enclosed in a sheath of muscular fibres. This difference can 
be most plainly recognized by preparing transverse sections, 
which may be made with a razor from tubes that have been har- 
dened in alcohol. The operation has already been described in 
the Naruratist for July, 1877, and to that the reader is referred. 
A section through the upper part is represented in Fig. 1. e 
single cells, each with its darkly 
stained and coarsely granular nu- 
They are all of about the same 
height, and form a single continuous 
layer. Every layer of this kind that 
lines any cavity whatsover is called 
an epithelium. A section through 
e SHES HPAP 
Fic. 1.—Section of upper part o : 
Vesicula seminalis. presents quite another appearance, 
though they form but a continuation of the same layer. 
this we learn that cells vary greatly in size, but the limits are 
much further apart than is here indicated. Outside the epithelium | 4 
is a very thick and powerful coat of muscular fibres, Mu, which 
cleus, lies close against its fellows. a : 
APN SY Sack OES a Pe REET Nee Ie ae 
