The milt of fishes, particularly that of the carp, analysed by Fourcroy and Vauquelin, contains— An oily and saponaceous matter, Gelatine, Albumen, Muriate of ammonia, Phosphate of lime, -- of magnesia, -- of potassa, of soda.
Phosphorus in such quantity as to emit light in the dark.
The semen is fluid in almost all animals. In some of the lower animals it is not so, but granular and crumbling. In the greater num ber of animals the fluid is of a white milky appearance and thinner consistence than in man, presenting in fishes the appearance of an emulsion of yolk of egg in milk.
In respect to its mode of discharge there are also many varieties dependent on the structure of the generative organs. In the lowest animals the testicle alone exists of the genital organs, and the secretory apparatus of this organ possesses a remarkably simple structure, consisting in many of a number of caeca or elongated follicles which pour the product of their secretion into a com mon duct. In the cuttlefish a very curious modification exists in the mode of discharge of the seminal fluid ; it being inclosed in small parcels in long-shaped transparent firm cases, somewhat like small phials. These cases are about three quarters of an inch in length, and are formed in the course of the vasa deferentia by an apparatus specially pro vided for the purpose : they are stopped at one extremity, and at the other are closed by a lid somewhat like the cork of a phial, be tween which and the main body of the case a spiral spring is interposed, so contrived that when the case is immersed in water the spring expands, forces off the top of the case, and allows the seminal fluid to issue from the interior.
We must refer to the anatomical articles for an account of the varieties of structure of the male generative organs in different animals. In some of those in which the vesicular semi nalcs are wanting, as in the familiar example of the dog, copulation is necessarily longer than in others. Very little is known as to the uses of the prostatic body or Cowper's glands. See GENERATION, ORGANS OF.
Spermatic animaleulcs.—The most remark able circumstance undoubtedly which is known respecting the spermatic fluid, is the almost constant existence in it of an immense number of minute moving bodies of the nature of In fusorial animalcule,—the well-known and celebrated srermatic animalcules, which, since the time of their first discovery in 1677, have excited the curiosity and speculative fancy of many naturalists.*
The spermatic animalcules have been found, at one time or other, in the semen of almost all the animals in which they have been sought font hut at that period of their life, and in that season of the year only, when the animals to which they belong arc fit for propagation. They are diminished in number, or even en tirely disappear, after very frequent emission of the seminal fluid. They almost always exist in the fluid secreted by the testicles, and very often in that of the seminal vesicles, into which they have doubtless been introduced along with the fluid of the testicles.
From these circumstances, as well as others to which we shall afterwards advert, there is good reason to believe, that the existence of seminal animalcules in the male product is in some way or other intimately connected with the integrity of its fecundating property ; if not, as some are inclined to hold, the essential cause of it.
The form, appearance, and size of the semi nal animalcule are diflbrent in almost every different animal, and in each species of the more perfect animals the kind of animalcule seems, like that of Entozoa, to be constant and d etenn i nate. While, therefore, these little crea tures, by their minute size and their general structure and appearance (so far as these are known), are distinctly animals of the infusorial kind, their residence in other living animals entitles them to be classed among the Entozoa. Baer considers them as most nearly allied to the Cercaria among the Infusoria, and gives them the very appropriate name of Sperma tozoa.
In what we have hitherto said of the seminal animalcules, we have drawn our description principally from what has been observed in quadrupeds and birds, but they differ consi derably from these in some of the inferior animals. Czermak• holds that these various forms may be referred to three principal heads, viz.:— 1. Cephaloidea, merely rounded bodies with out tails, existing in fishes and some Annelida.