Tur Hog Lovusre ~ 705 
The remaining ‘mesodermal structures are slender tubes varying in 
diameter. Seen in cross section (Plate LXIII, 3) the inner layer of their 
wall is composed of epithelial cells resting on an exceedingly fine basement 
membrane. Outside this is a thin, structureless layer, the true nature 
of which has not been determined. The anterior half of the ejaculatory 
duct is surrounded by a strong wall of circular muscle fibers, among 
which are also, toward the posterior end, strands arising at right angles 
to the duct wall and passing to the outer edge of the circular fibers. Nuttall 
(1917 a:307) attributes this strong development of muscle to the force 
necessary to drive the spermatic fluid down the long, slender part of 
the duct. 
The epithelial cells lining the vasa deferentia are small and somewhat 
flattened, and have a straight surface in the lumen. The anterior sections 
of the seminal vesicles act as a reservoir for the developed spermatozoa, 
and there, as in the sections of the vasa deferentia, they can be seen. The 
epithelium of the region is regular and columnar, and the nuclei, which 
are circular and have a well-defined nucleolus, lie near the base of the 
cells, of which the cytoplasm contains many dark-staining granules. 
Lower in the tubes the cells lose their clearly defined inner borders and 
appear finely granular, while a secretion which stains a deep pink with 
eosin surrounds the spermatozoa. This secretion soon takes a definite 
form and is oval in outline, and, in appearance, not unlike a cross section 
of an orange or the illustration of the ‘“‘ Magenscheibe ”’ given by Landois 
(1865a: Pl. IV, fig. 8), and it contains minute vacuoles (Plate LXIV, 6). 
These suggest spermatophores, but in section no spermatozoa could be 
seen within them. Still farther along in the vesicles the inner borders of 
the cells project into the lumina as blunt, thumblike processes, which 
are slightly pink in sections stained with hematoxylin and eosin, while 
the remainder of the cell is dark blue. No cell walls are seen and the cells 
are evidently in active secretion. The clearly defined “ spermatophores ”’ 
now become markedly vacuolated and gradually lose all semblance of a 
definite form. Probably this secretion acts as a solvent. In the anterior 
part of the muscular section of the ejaculatory duct the cells are small, 
but in the posterior part the epithelium is much thickened and has a 
markedly glandular appearance. From many of the cells of the vesicles 
and the ejaculatory duct, slender processes project into the canals and 
even directly into the central mass of secretion, while in some parts of 
