tation, and guard against the accidental displacement of the egg. Some of these follicles are frequently distended with their secretion, and project, as small, hard, rounded eminences, from the surface of the mucous membrane. In this condition they are sometimes designated by the name of "ovula Nabothi," owing to their having been formerly mistaken for eggs, or ovules.

The cavity of the cervix uteri is terminated below by a second constriction, the "os externum." Below this comes the vagina, which constitutes the last division of the female generative pas

sages.

The accessory female organs of generation consist therefore of ducts or tubes, by means of which the egg is conveyed from within outward. These ducts vary in the degree and complication of their development, according to the importance of the task assigned to them. In the lower orders, they serve merely to convey the egg rapidly to the exterior, and to supply it more or less abundantly with an albuminous secretion. In the higher classes and in the human subject, they are adapted to the more important function of retaining the egg during the period of gestation, and of providing during the same time for the nourishment of the young embryo.

CHAPTER IV.

ON THE SPERMATIC FLUID, AND THE MALE ORGANS OF GENERATION.

THE mature egg is not by itself capable of being developed into the embryo. If simply discharged from the ovary and carried through the oviducts toward the exterior, it soon dies and is decomposed, like any other portion of the body separated from its natural connections. It is only when fecundated by the spermatic fluid of the male, that it is stimulated to continued development, and becomes capable of a more complete organization.

The product of the male generative organs consists of a colorless, somewhat viscid, and albuminous fluid, containing an innumerable quantity of minute filamentous bodies, termed spermatozoa. The name spermatozoa has been given to these bodies, on account of their exhibiting under the microscope a very active and continuous movement, bearing some resemblance to that of certain animalcules.

The spermatozoa of the human subject (Fig. 167, a) are about abo of an inch in length, according to the measurements of Kölliker. Their anterior extremity presents a somewhat flattened, triangular-shaped enlargement, termed the "head." The head constitutes about one-tenth part the entire length of the spermatozoon. The remaining portion is a very slender filamentous prolongation, termed the "tail," which tapers gradually backward, becoming so exceedingly delicate towards its extremity, that it is difficult to be seen except when in motion. There is no further organization or internal structure to be detected in any part of the spermatozoon; and the whole appears to consist, so far as can be seen by the microscope, of a completely homogeneous, tolerably firm, albuminoid substance. The terms head and tail, therefore, as justly remarked by Bergmann and Leuckart,' are not used,

Vergleichende Physiologie. Stuttgart, 1852.

when describing the different parts of the spermatozoon, in the same sense as that in which they would be applied to the corresponding parts of an animal, but simply for the sake of convenience; just as one might speak of the head of an arrow, or the tail of a comet.

In the lower animals, the spermatozoa have usually the same general form as in the human subject; that is, they are slender filamentous bodies, with the anterior extremity more or less enlarged. In the rabbit they have a head which is roundish and flattened in shape, somewhat resembling the globules of the blood. In the rat (Fig. 167, b) they are much larger than in man, measur

ing nearly of an inch in length. The head is conical in shape, about one-twentieth the whole length of the filament, and often slightly curved at its anterior extremity. In the frog and in reptiles generally, the spermatozoa are longer than in quadrupeds. In the Menobranchus, or great American water-lizard, they are of very unusual size (Fig. 167, c), measuring not less than of an

inch in length, about one-third of which is occupied by the head, or enlarged portion of the filament.

The most remarkable peculiarity of the spermatozoa is their very singular and active movement, to which we have already alluded. If a drop of fresh seminal fluid be placed under the microscope, the numberless minute filaments with which it is crowded are seen to be in a state of incessant and agitated motion. This movement of the spermatozoa, in many species of animals, strongly resembles that of the tadpole; particularly when, as in the human subject, the rabbit, &c., the spermatozoa consist of a short and well defined head, followed by a long and slender tail. Here the tail-like filament keeps up a constant lateral or vibratory movement, by which the spermatozoon is driven from place to place in the spermatic fluid, just as the fish or the tadpole is propelled through the water. In other instances, as for example in the water-lizard, and in some parasitic animals, the spermatozoa have a continuous writhing or spiral-like movement, which presents a very peculiar and elegant appearance when large numbers of them are viewed together.

It is the existence of this movement which first suggested the name of spermatozoa to designate the animated filaments of the spermatic fluid; and which has led some writers to attribute to them an independent animal nature. This is, however, a very erroneous mode of regarding them; since they cannot properly be considered as animals, notwithstanding the active character of their movement, and the striking resemblance which it sometimes presents to a voluntary act. The spermatozoa are organic forms, which are produced in the testicles, and constitute a part of their tissue; just as the eggs, which are produced in the ovaries, naturally form a part of the texture of these organs. Like the egg, also, the spermatozoon is destined to be discharged from the organ where it grew, and to retain, for a certain length of time afterward, its vital properties. One of the most peculiar of these properties is its power of keeping in constant motion; which does not, however, mark it as a distinct animal, but only distinguishes it as a peculiar structure belonging to the parent organism. The motion of a spermatozoon is precisely analogous to that of a ciliated epithelium cell. The movement of the latter will continue for some hours after it has been separated from its mucous membrane, provided its texture be not injured, nor the process of decomposition allowed to commence. In the same manner, the movement of the

spermatozoa is a characteristic property belonging to them, which continues for a certain time, even after they have been separated from all connection with the rest of the body.

In order to preserve their vitality, the spermatozoa must be kept at the ordinary temperature of the body, and preserved from the contact of the air or other unnatural fluids. In this way, they may be kept without difficulty many hours for purposes of examination. But if the fluid in which they are kept be allowed to dry, or if it be diluted by the addition of water, in the case of birds and quadrupeds, or if it be subjected to extremes of heat or cold, the motion ceases, and the spermatozoa themselves soon begin to disintegrate.

The spermatozoa are produced in certain glandular-looking organs, the testicles, which are characteristic of the male, as the ovaries are characteristic of the female. In man and all the higher animals, the testicles are solid, ovoid-shaped bodies, composed principally of numerous long, narrow, and convoluted tubes, the "seminiferous tubes," somewhat similar in their general anatomical characters to the tubuli uriniferi of the kidneys. These tubes lie for the most part closely in contact with each other, so that nothing intervenes between them except capillary blood vessels and a little areolar tissue. They commence, by blind, rounded extremities, near the external surface of the testicle, and pursue an intricately convoluted course toward its central and posterior part. They are not strongly adherent to each other, but may be readily unravelled by manipulation, and separated from each other.

The formation of the spermatozoa, as it takes place in the substance of the testicle, has been fully investigated by Kölliker. According to his observations, as the age of puberty approaches, beside the ordinary pavement epithelium lining the seminiferous tubes, other cells or vesicles of larger size make their appearance in these tubes, each containing from one to fifteen or twenty nuclei, with nucleoli. It is in the interior of these vesicles that the spermatozoa are formed; their number corresponding usually with that of the nuclei just mentioned. They are at first developed in bundles of ten to twenty, held together by the thin membranous substance which surrounds them, but are afterward set free by the liquefaction of the vesicle, and then fill nearly the entire cavity of the seminiferous ducts, mingled only with a very minute quantity of transparent fluid.

In the seminiferous tubes themselves, the spermatozoa are always