392 PHILOSOPHY OF ZOOLOGY. 
Besides these organs, there are others which appear to 
be necessary towards perfecting the seminal fluid. ‘These 
are the Seminal Vesicles, the Prostate Gland, and Cowper's 
Glands. The Seminal vesicles are two in number, corre- 
sponding with the spermatic ducts*. In some cases their 
cavity is simple, while in others it is divided into numerous 
sacs, united together by cellular substance. The walls of 
these vesicles are, in some animals, thin and simple, and 
lined with a continuation of the mucous membrane of the 
urethra; while in others they are thick and glandular, and 
are evidently destined for secretion. These vesicles termi- 
nate in the urethra, either by canals which are common to 
the spermatic ducts, or by orifices peculiar to themselves. 
The seminal vesicles are wanting im many quadrupeds. 
Their presence does not seem to be regulated by any uni- 
form plan, or to be exhibited in any peculiar habits. Their 
use, where they do exist, has not been satisfactorily deter- 
mined. By some, they are considered to be receptacles of 
the spermatic fluid; while by others they are regarded as 
destined to secrete a fluid peculiar to themselves. This 
last opinion is rendered probable by the judicious remarks 
of Hunter +, and confirmed by the whole history of their 
structure, contents, and terminating canals. That they 
are still connected with the reproductive system, is indicat- 
ed by their increased size during the season of love. 
The Prostate Gland is situated at the commencement 
* The vesicule acecesorie of Cuvier, are membranous tubes, varying in 
number, adhering to the sternal side of the vesicles, or situated around the 
base of the urethra. They are filled with the same fluid as the vesicles, and 
empty their contents into the urethra by a common duct, or by a separate 
opening. They are very obvious in the mole and hedgehog. 
‘++ ‘* Observations on certain parts of the Animal Economy.” London, 
1786, p. 27,-—42. 
