L. E. Robinson and J. Davidson 
413 
The Genital Organs of the Male. 
Plate XXVII, see also Part II, Plates XV and XVI. 
The genital organs of the male comprise the following parts : 
1. The Testis. 3. The Seminal Vesicle. 
2. The Vasa Deferentia. 4. The Ductus Ejaculatorius. 
5. The Accessory Glands. 
The Testis. 
’ Plate XXVII, fig. 1 , tes. 
The testis is situated in the posterior part of the body, in a position, 
corresponding precisely, in its relations to the surrounding organs, with 
that of the ovary in the female. It consists of a slightly irregular, more 
or less convoluted, flattened tube of a yellowish-white colour, smaller 
in diameter than the ovary, but of about equal length— i.e. approxi¬ 
mately one-half of the body width. 
The outer wall of the testis is formed by a thin sheath of connective 
tissue, within which, in young immature males, a single layer of 
epithelial cells of large size appears. These cells are the spermatogonia, 
which, as the testis developes, proliferate, passing by two successive 
maturation divisions through the spermatocyte stage to the final or 
spermatid form. Each spermatogonial cell thus gives rise to four 
spermatids, which are transformed without further division into sperma¬ 
tozoa. As usually seen in sections, the lumen of the greater part of 
the testis is packed with spermatids, which are at first enclosed in 
“ pockets ” formed by thin partitions of connective tissue which extend 
from the investing connective tissue sheath of the testis. As the 
spermatids increase in size, the “ pockets ” break down, and the now 
free spermatids pass from the lumen of the testis to the vas deferens 
where they rapidly assume the elongated form of the mature 
spermatozoa. 
The Vasa Deferentia. 
Plate XXVII, figs. 1-2, vd., vd'. 
The vasa deferentia are a pair of long ducts which issue from the 
lateral extremities of the testis, and, after a tortuous course, open into 
an unpaired median seminal vesicle. 
The diameter of these ducts shows a remarkable range of variation 
in the different sections of their course. The first section of the 
Parasitology vi 
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