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.
(2013). In tracing the development of the generative apparatus through the different orders of Reptiles, the student will not fail to observe many beautiful illustrations of progressive improvement.
* Vide Cyclopedia of Anatomy and Physiology, art. Amphibia, by Professor Bell, p. 104.
(2014). The finny tribes, incapable of social intercourse, were content with the simple extrusion of their eggs into the sea, leaving them to be impregnated by the casual approach of a male of the same species; but even in the Amphibious reptiles some steps are gained in associating the sexes with each other; and although the eggs are still impregnated out of the body of the mother, in the Frog this is accomplished in eceitu, and not subsequent to their expulsion.
(2015). Frogs, during the breeding-season, are found to pair, and the male having selected his mate mounts upon her back, clinging to her with unwearying pertinacity during the whole period of oviposition, and vivifying her eggs by the aspersion of the seminal secretion as they are successively expelled in long gelatinous chains. During this protracted embrace the male Frog is assisted in retaining his hold by the development of a peculiar papillose structure upon the first toes of the fore-feet, which disappears at the end of the time appropriated to reproduction. Of course no intromittent apparatus is as yet required, and we may naturally expect to find the male organs still exhibiting great simplicity of construction.
(2016). The testes and their excretory ducts, in fact, are the only parts as yet met with; but the anatomy of these parts, although most accurately investigated by Swammerdam upwards of a century ago, is still very generally misunderstood. The testicles are situated in the loins, surrounded by several tongue-like masses of fat presenting a peculiar granulated appearance. Each testis is invested by a delicate capsule, and on removing this very carefully, the entire viscus is seen to be made up of short caeca, the blind extremities of which alone appearing at the periphery of the organ caused Cuvier to describe it as being "an agglomeration of little whitish grains interwoven with bloodvessels." The semen elaborated by these caeca is taken up by several small excretory ducts that pierce the kidney, in the immediate vicinity of which the testis lies, and open into the ureter, that here forms the common excretory duct, whereby the urine as well as the seminal fluid is discharged, both escaping into the cloaca at a little distance from the orifice of the allantoid bladder, to be ultimately ejected through the vent.
(2017). Neither is the generative system of the female Frog less worthy of notice. The ovaria resemble in their essential structure those of the Lamprey (§ 1846); only they are much less extensive, consisting of a few festoons of the highly vascular membrane wherein the ova are secreted, fixed at the pelvic extremity of the abdominal cavity. On each side of the body is a long and very tortuous oviduct, which when unravelled is found to be many times the length of the animal. The fimbriated commencement of this oviduct is firmly bound down by folds of peritoneum in the immediate vicinity of the pericardium, and, of course, as remote as possible from the ovary; it therefore becomes a question of no inconsiderable interest to determine the manner in which the ova are conveyed from the ovarian nidus to the orifice of the oviduct. It is obvious that they must first break loose into the abdominal cavity, as we found them to do in the Lamprey and the Eel, and that at length, having made their way into the neighbourhood of the pericardium, they are seized by the patulous extremity of the Fallopian tube, and thus conveyed out of the body.
As the ova make their transit through the oviduct they become imbedded in a tenacious albuminous secretion, and are at length lodged in a dilated portion of the tube, to which the name of uterus has been very improperly given, preparatory to their expulsion through the cloaca. After the eggs have been discharged into the surrounding water, the albuminous mass in which they are imbedded swells considerably; and when the young tadpoles are hatched, this material no doubt serves to nourish them during the earlier period of their existence.
(2018). In the Newt (Triton) impregnation takes place internally, although the male is still without any rudiment of an intromittent apparatus, so that we are compelled to believe that in the case of these Amphibia the simple ejection of the male fluid into the water in the vicinity of the female is sufficient to ensure its admission to the ova while still in the oviduct. An improvement is likewise visible in the construction of the internal viscera subservient to generation; and a vas deferens, quite distinct from the ureter, makes its appearance. In the male Salamander (Triton cristatus) the testis during the breeding-season consists of two pyriform masses, from which the seminal ducts (fig. 352, c c) are derived. These soon unite to form a single convoluted tube (d), through which the semen is conveyed into the cloaca. The kidneys (n) and their excretory ducts (i i) are here placed considerably further back; but the ureters terminate in the cloaca at the same point (m) as the vasa deferentia. Two other large glands (o o) are apparently connected with the generative functions, and their excretory ducts likewise open into the cloacal outlet.
Fig. 352. Generative organs of male Salamander.
(2019). In the female Triton, as also in the Proteus and Siren, the ovaria and oviducts offer precisely the same arrangement as that met with in the Frog, already described *.
(2020). In the Ophidian, Chelonian, and Saurian orders, the testes of the male sex are situated in the loins; and in fact they occupy the same position throughout the oviparous Vertebrata: they offer no peculiarity of structure, only differing from those of the Prog in the increased length of the now contorted seminal caeca of which they are essentially composed. From each testis a long and flexuous vas deferens conducts the semen into the cloaca. Here, however, in these more elevated forms of the Reptilia, we have another important addition to the male sexual apparatus - instruments being given to facilitate the impregnation of the female during that union of the sexes which now becomes essential to fecundity. The earliest appearance of the copula-tory organ is seen in Serpents and in the Lizard tribes; and in such reptiles it will be observed that the penis is rather a provision for securing the juxtaposition of the sexual apertures of the male and female than an instrument of intromission. The two lateral halves of the penis (or corpora cavernosa, as we shall have to call them hereafter, when they become conjoined in the mesial line) are as yet quite separate, and placed at each side of the cloaca! fissure, from which they protrude when in a state of erection, so that there appear to be two distinct organs of excitement, or, more properly speaking, of prehension; for each division, being of course imperforate, is covered with sharp spines, and is obviously rather adapted to take take firm hold of the cloaca of the female than to form a channel for the introduction of the seminal fluid.