n of this gland is conveyed into the urethra by
numerous short ducts, known as the _prostatic ducts_. Behind the
prostate, at the base or fundus of bladder, are the paired _seminal
vesicles_. The duct of the seminal vesicle joins the _vas deferens_ of
the same side (both functionally and embryologically the seminal vesicle
is no more than a diverticulum of the vas deferens); passing on under
the name of the _common seminal_ or _ejaculatory duct_, the canal opens
into the prostatic portion of the urethra (the orifices of the two
common seminal ducts are in the folds of mucous membrane forming the
right and left lateral margins of the _prostatic utricle_ or _uterus
masculinus_). These ducts convey the secretion of the testicles into the
urethra along which canal it passes to the exterior. Behind the
posterior part of the urethra, but distal to the prostate gland, are
situate also the paired _glands of Cowper_, or _suburethral glands_,
whose excretory ducts likewise open into the urethra. There are glands
also in the walls of the seminal vesicles, the vasa deferentia, and the
urethra; the urethral glands are commonly known as the _glands of
Littre_.

As previously mentioned, it is in the testicles that the secretion
necessary for the reproductive act is prepared. This secretion is
evacuated during sexual intercourse, and also during masturbation and
involuntary seminal emissions. The testicular secretion is a tenacious
fluid. When examined microscopically, it is seen to contain countless
spermatozoa, structures about 50 [Greek: m] (1/500 inch) in length, with
a thick head and a long filiform tail. They represent the male
reproductive cells, which during coitus are introduced into the interior
of the female reproductive organs; a single spermatozoon unites with the
ovum of the female to form the fertilised ovum. The spermatozoa are
formed in the walls of the convoluted seminiferous tubules. The cells
lining these tubules are of several different kinds (although in
childhood they are not differentiated as they are after the puberal
development has taken place). One variety of these cells, the
_spermatogonia_, undergo an increase of size at puberty, and from these
spermatogonia, after passing through several intermediate transitional
stages, the spermatozoa are formed.

It was formerly believed that the sole function of the testicles was the
production of the spermatozoa; recently, however, the opinion has gained
ground tha