On examining the external coverings of Hydra, we shall readily be enabled to con vince ourselves of the formation of these organs. The most different stages of de velopment may here be seen, viz. developed prickles, either free or still enclosed by a cell membrane, from which the organ it self, and especially the fibre enclosed in its interior, recedes more and more, until it finally appears as a mere simple nucleus. In several Planarim the organs are con tained, in an imperfect state, in considerable numbers in one common cell. The nuclei in the interior of the cells have therefore multiplied here, as in the seminal cells of the vertebrata.
_ Organization of the spermatozoa,— At the period when the spermatozoa were still con sidered as individual animated creatures, it was natural that those qualities should be sought for, which distinguish animals gene rally; end it was frequently asserted that the distinct traces of an internal organization had been found in them. Even Leuwenhoek*, the oldest observer of these structures, de scribes in the body of the spermatozoa of the ram and of the rabbit, indications which were subsequently interpreted by _Ehrenberg -I and Valentin t to be intestines, stomachic vesicles, and even generative organs. Other histologers, for instance, Schwann and Henle, thought themselves justified in calling a dark spot, which shows itself occasionally in the body of the spermatozoon in men, but which is decidedly a mere accidental formation, as a suctorial cavity. But all these statements are now no longer believed in, as our present knowledge of the developement of these form ations has entirely removed the idea of their parasitic nature. Indeed the subject requires no further refutation, as an unprejudiced ob servation will prove that the spermatozoa are every where void of a special organization, and consist of an uniform homogeneous sub stance, which exhibits, when examined by the microscope, a yellow amber-like glitter. The above mentioned investigators have by this time undoubtedly seen their error.
Motions of the spermatozoa.— The opinion of an internal organization of the developed seminal elements was not a little supported by the various remarkable phenomena of motion, which were frequently perceived in them. In former times, when people had no idea of the existence and extent of the so called automatic phenomena of motion, which take place without the intervention or in fluence of the nervous system ; when nothing was known of the motion, very similar to a vo luntary one, which exists even in plants; this movement was certainly calculated to place the independent anirnal nature of the skrrnatozoa almost beyond a doubt. But it is different
now. We now know tbat motion is not an exclusive attribute of animals, and that an in ference respecting the animal nature of the formations in question, however similar the motion observed in them may be to that of animal organizations, is a very unsafe and venturesome one. We know that certain elementary constituents, animal as well as vegetable, possess a power of movement, and that they even retain it for some time after having been separated from the organisms to which they belonged. We only here need remind our readers of the so-called ciliated epithelia, the severed cells of which swim about in the fluid surrounding them, and which, when in this state, have not unfre quently, and that even quite recently, been considered as independent animals §; how, further, the spores of the algm possess motion by, the aid of a ciliated investment*, or of a single or manifold long whip-like fibre, until they eventually become fixed, and develop themselves into a DOW plant.t Such spores as these 'nay be found described and illustrated in the well-known magnificent work of Ehren bem, classified as Infusoria under the groups of Monadina, Volvocina, &c.
Under such circumstances we may consider ourselves perfectly justified in declaring every attempt to prove the parasitic nature of the spermatozoa, by the characteristic of their peculiar motions, as futile and inadmissible. Developement, structure, and composition are the decisive characteristics in this respect, and these prove the fructifying elements of the semen to be mere elementary constituents of the body in which they are formed. The motions of the spermatozoa are therefore in their essence identical with the above men tioned automatic motions of cilia, &c. But the knowledge of the movement of the sperma tozoa will always be interesting and impor tant ; because, of all these phenomena, it is undeniably most closely connected with the locomotive motions of animals.