778 Wisconsin Academy of Sciences, Arts, and Letters. 
tions of the epithelium which give to the lumen very odd shapes, 
these outgrowths finally take the form of a solid central core. 
This mass of cells passes entirely through the vas deferens and 
finally fuses again with the regular epithelial layer of the 
wall. A transverse section through any part of either vas 
deferens (fig. 42) will show this central core of cells and also 
that the sperms occupy entirely or in part the space between 
it and the epithelium of the true wall. Longitudinal sections 
of the vas deferens show that the central core is now and 
then supported by strands of cells which connect it to the 
epithelium. 
In transverse section the wall of the vas deferens is seen to 
be composed of tw r o layers. The inner of these, the epithelium, 
is a single layer of columnar cells each cell containing an ir¬ 
regularly ovoid nucleus (fig. 43). The outer layer of the wall 
is not so thick as .the epithelium; it is composed of from one 
to three layers of cells, these are generally flattened but where 
there is a single layer this is mot the case. If two or more 
layers of the cells are present the inner layer is much more 
flattened than the others. The nuclei of these cells are small 
and their form varies with the shape of the cell. At the place 
where the vas deferens leaves the testis there is more or less 
fat present; some of these small fat masses can be traced down 
over the vas deferens into this outer layer. Where the trach¬ 
eae in any way touch the vas deferens the fat which may sur¬ 
round them can be seen to connect with these fat cells which 
surround the latter. This layer surrounding the vasa defferen- 
tia is a continuation of these fat cells. 
Following in serial sections the vas deferens it is seen that 
where it widens to form the seminal vesicle the structure of 
the w T all changes. In the vesicle (fig. 44) the epithelial layer 
has changed only in the cells being shorter and that the cell 
boundaries are'very difficult to find. The fat cells as a layer 
Lave disappeared and in their place we find a wider layer of 
muscle fibres running in various directions. Along the free 
surface of the epithelium a cuticular layer is present. 
