This section is from the book "General Outline Of The Organization Of The Animal Kingdom, And Manual Of Comparative Anatomy", by Thomas Rymer Jones. Also available from Amazon: A General Outline of the Animal Kingdom and Manual of Comparative Anatomy.
Fig. 419. Male generative apparatus of the Hedgehog.
(2460). The quantity of the seminal fluid furnished by the testes is very small, as must be evident from the extreme narrowness of the duct through which it passes into the urethra. Nevertheless, as the impregnation of the female now requires the forcible injection of this fluid, it is absolutely requisite to increase the bulk of the vivifying secretion, in order to enable the muscles that embrace the urethral tube efficiently to expel it. For this purpose additional glands are given, whereby different fluids are poured into the urethral cavity, apparently for the sole purpose of diluting the spermatic liquor, and thus forming a vehicle for its expulsion. These succenturiate glands, as they are named, are not found in any oviparous animal; but in the Mammal such is their size and importance that there may be just reason for supposing them to exercise a more important office than that usually assigned to them by physiologists; and this supposition seems to obtain additional weight when we consider the great diversity of structure that they exhibit in different quadrupeds.
(2461). The vesiculce seminales are the first of these accessory secreting organs that require our notice. In Man, the seminal vesicles, as they are erroneously termed, resemble two membranous reservoirs, situated beneath the neck of the bladder, and were once supposed to be receptacles for containing the semen. When opened, however, they are found to be composed of the windings of a very sinuous secreting surface; and as their excretory ducts open into the urethra in common with the vasa deferentia, they obviously add the fluid that they elaborate to the secretion of the testes.
(2462). But notwithstanding their apparent importance in the human species, these organs do not exist at all in by far the greater number of Carnivora; neither are they found in the Ruminants, nor in the cetaceous Mammals.
(2463). In other quadrupeds, on the contrary, they are found, and their proportionate size is extremely remarkable. This is specially the case in the Rodent tribes and among the Insectivora. In the Hedgehog, for example, their bulk is enormous. In this creature they form two large masses (fig. 419, a, cc), each composed of four or five bundles of long and tortuous secerning vessels folded upon themselves in all directions, and pouring the product of their secretion into the urethra by two ducts (fig. 419, b, c c), quite distinct from the vasa deferentia.
(2464). The prostates are the next succenturiate glands, superadded to the essential generative organs of the placental Mammals; and so diverse is their structure in different tribes, that it is not always easy to recognize them under the varied forms that they assume.
(2465). In Man the prostate is a solid glandular mass, that embraces the commencement of the urethra, into which it discharges its secretion by numerous small ducts; and this is the most common arrangement throughout the Mammiferous orders.
(2466). In Ruminants, Solipeds, and in the Elephant, there are two or even four prostates, of a very different kind, each gland having a central cavity, into which smaller cavities open by wide orifices. In these creatures, therefore, the prostatic secretion accumulates in the interior of the gland, from whence it is conveyed into the urethra by appropriate excretory canals.
(2467). In most of the Rodentia, in the Mole, and in the Hedgehog, the structure of the prostate is so peculiar that many distinguished comparative anatomists refuse to apply the same name to organs that obviously represent the gland we are describing, preferring, with Cuvier, to call them "accessory vesicles".
(2468). In the Hedgehog, the prostate is replaced by two large masses (fig. 419, a, d d), each composed of parallel, flexuous, and branched tubes, all of which unite into ducts common to the whole group, whereby the fluid elaborated is conveyed into the urethra through minute orifices (fig. 419, b, e e).
(2469). A third set of auxiliary secreting bodies, very generally met with, are called by the name of "Cowper's glands." These in our own species are very small, not exceeding the size of a pea; but in many quadrupeds they are much more largely developed. In the Hedgehog (fig. 419, a,f) they are obviously composed of convoluted tubes, and their ducts open by distinct apertures (b, g g) into the floor of the urethra.
(2470). The canal of the urethra, through which the urine as well as the generative secretions are expelled from the body of the male Mammal, is a complete tube, and no longer a mere furrow, as we have seen it to be in all the Ovipara possessed of an intromittent apparatus. It extends from the neck of the bladder to the extremity of the penis; but in this course, owing to its relations with the surrounding parts, it will be necessary to consider it as divisible into two or three distinct portions, each of which offers peculiarities worthy of remark. The first part of the urethral tube is not unfrequently, as in the human subject, more or less completely surrounded by the prostate gland, and in such cases merits the name of "prostatic portion;" but where, as in the Hedgehog, the prostates do not enclose the commencement of the canal, this division of the urethra does not exist.
(2471). The second is the "muscular portion," extending from the prostate to the root of the penis; and it is into this part that all the generative secretions are poured from their respective ducts (fig. 419,b,b, c, e, g, h.) Externally this division of the urethra is enclosed by strong muscles (fig. 419, a, i i), which by their convulsive contractions forcibly ejaculate the different fluids concerned in impregnation, and thus secure an efficient intromission of the seminal liquor into the female organs.