We must not, however, lose sight of the fact, that these motions are not possessed in equal perfection by all spermatozoa, but that in many cases they are scarcely visi ble and hardly equal the motions of the cilia. Indeed there are many spermatozoa which are perfectly motionless, particularly all those forms which owe their immediate origin to a metamorphosis of the nucleus, or of the wall of the primary cells. Only those spermatozoa which have been produced by an endogenous and new developement are capable of independent motions, and even not every one of these. No such movements have as yet been perceived in the spermatozoa of the Malacostraca (Isopoda and Amphipoda). They appear motionless and rigid. The same holds good with regard to the body of the spermatozoa when it has a short, round, or pyriform shape. It never then participates in the motions, which are in such cases altogether effected by the thinner, whip like, caudal extremity. It is different, how ever, with those spermatozoa which pos sess a cylindrical body. The body here par ticipates in the motion ; at least very fre quently, as, for instance, among the scaly amphibia, amon,,,, the birds (excepting among the singing birds), &c. But the motions of the body are less rapid, energetic, and various than those of the tail. They are principally limited to a bow-shaped curvature, similar to the motion of the Vibriones, which, like the Monadina, belong to the vegetable kingdom, and may undergo a further developement into fibrous fungi, In order to observe the movements of the spermatozoa properly, they ought to be in vestigated under different circumstances. On putting a drop of thick semen from the vas deferens under the microscope, a slow mo tion only can usually be observed in the accuinulated masses of spermatozoa. They present an appearance as if they had some difficulty in disentangling themselves from the tough fluid by which they are sur rounded. On adding blood serum to it to dilute the mass, the movement becomes more lively,either instantaneously or gradually. Se parate spermatozoa writhe once or twice, turn round on their axis, lash with their tail, and creep about in all directions over the field. The motion gradually imparts itself to greater numbers. Here and there, simultaneously all the individuals of a group begin to move; or particular parts of the mass commence the movement. The remainder perhaps exhibit no motion, and sometimes this quiescent state is permanent.
If the movement of the spermatozoa be rapid, it assumes, for the most part, an accu rate rhythm like a pendulum. The fili form tail vibrates like a whip, and the small corpuscle or head follows the impulse. Frequently a peculiar trembling, dancing, or jumping is exhibited by the hitter when the rest of the spermatozoon remains fixed and un moved. A serpen tine creeping in al/ directions is produced during a slow motion, and is caused by an undulating contraction of the caudal appendix. These undulating rnotions are perhaps the most frequent which the spermatozoa (and even the thread-like forins which possess no visible body) present to our view. They often move in one straight direc tion,. without turning aside, and altogether in such a way and with such a regularity as to resemble the locomotive motions of many of the lower anhnals.
The same regularity is met vvith in the motions of the long and rigid spermatozoa with a spiral body among the singing birds, which very frequently turn rapidly round their axis, and thereby advance with a screw-like or boring movement. Pendulum-like lateral motions are but rare.
Very peculiar and different are the motions of the spermatozoa in the Salamanders, which usually lie wrapped up like a watch spring, flat on a level. For a time they remain quiet until suddenly, by fits and starts, a trembling motion takes place, by which they turn them selves round in a circle, pretty nearly on the same spot. Some few (as the Bornbinator) stretch themselves out, and travel with a slow undulating motion over the field of the microscope. The most remarkable pheno menon, however, consists in a peculiar wave like motion on the surface, and which is solely caused by the rapid succession of un dulating motions. We have also perceived a perfectly similar undulating motion in the very long, "coiled-up spermatozoon of Geo philus, which is occasionally so powerful as to cause the whole fibre to be moved round in a circle.
The normal movetnents of the spermatozoa just described must be distinguished from various other remarkable and irregular pheno mena of motion which are perceived on treat ing them with water, particularly in the long and hair-like spermatozoa of the Insects, Gas teropoda, Helmintha, and Cirripeda, and also sometinaes, although in a slighter degree, in those of the Reptilia and Mammalia. S'iebold* was the first who estimated these latter phe nomena at their proper value, attributing to them their real cause, viz. the hygroscopic quality of the spermatozoa.
These phenomena take place only on the addition of fresh water, whilst sea water exercises but little influence on the sper matozoa, which may be accounted for by the difference in the saline constituents of these fluids. This fact, however, is of the greatest importance, in a physiological point of view, because the fecundation of' the ova in many marine animals does not take place by copulation, but is accomplished through the transfer of the spermatozoa by means of the sea water, and the influence of tbis me dium should not be such as to destroy the power of motion on the part of the sperma tozoa. In cases -where the fecundation takes place in the same manner in fresh water, for instance in the muscles, the spermatozoa are but slightly hygroscopic, so that their in tegrity remains undisturbed. - These abnormal phenomena of motion, caused by the influence of water, exhibit something similar to that which is seen in a rope turned by a wheel in a rope yard. The spermatozoa roll themselves out in larger or smaller windings, and form simple or com pound coils of the most variable kinds. Fre quently they turn back again after some time, and re-assume their original shape ; they fre quently also remain in the position they have at first assumed. In short, changes take place every moment. When the fibres lie in a straight position, a number of coils are sud denly produced; but they disappear equally as quickly, and it is only after some hours, when all the spermatozoa have rolled themselves into these coils, that the movements finally cease.