The description we have just now given may, at all events, be sufficient to prove of what a merely subordinate signi6cance are -these diflerences in the histolosical arrange ments of the formative elements in the seminal fluid. By a series of intermediate starres, we can almost every where readily trace die con nexion in which the grrangement of the vesi cles of developement stands with the simple primitive spermatic cell. Such a relation, however, is not only interesting on account of its enabling us to recognise an internal typical structure anti developement of the seminal contents, and that in spite of their external variety, but also because we thereby discover that the primitive form of the male procrea tive elements is precisely the same — namely, a simple cell— as that of the female gene rative product, which is designated " the ovum.' Having thus, by our preceding researches, arrived at the result that the developement of the spermatozoa always and everym,here ori ginates from the same primitive formation, namely, from the simple cell, another question now arises viz. the question respecting the relation of' this simple cell to the epithelial lining of the seminal tubes.
This claims our attention the more, as our conception of the epithelium, within a re cent period, begins to be more and more indefinite, owing to the accumulation of ob servations, by which the so-termed epithelial cells of the glands have been proved to be mere vesicles of secretion, the workshops for the preparation or expulsion of the-products of secretion.
The recognition of the connexion of the spermatic cells with the real epithelial cells is rendered very difficult by the various meta morphoses of the former in the tubuli seminiferi. Nevertheless, some observations that have been made may perhaps already justify the inference that the simple spermatic cells are, in many instances, at least. identical with the so-called epithelial cells of the se minal tubes.
This appears with particular distinctness in the Gasteropoda, in which Meckel* and Jai liker have already assumed such a relation, without, however, pronouncing it with that degree of certainty which our observations enable us to do. We may as readily con vince ourselves of this fact in the Annelida, in Hirudo or Ascaris, as also in the In sects, Spiders, and Arthrostracans : it being evident in all of them that the sperniatic cells constitute the only vesicular contents of the testicles, and form, in their primitive shape, a complete epithelial layer, the ele ments of which frequently even assume a polygonal shape by close adaptation to each other.
This connexion is, however, least distinct among the higher Vertebrata; in which, inde pendently of the spermatic cells which exist free in the semen of the seminal canals, there likewise occurs a special and generally well developed stratum of epithelial cells, which are distinguished from the former by size and appearance. But this arrangement is only to be met with during the period of generative maturity. Previous to it, free spermatic cells do not exist, and the canals of the testicle have then uniform contents, con sisting of small cells of rh, of a line in dia meter, in which one or two small granules are contained. We have not been able to trace the history of the real seminal cells, but we do not consider it as altogether impro bable that they are produced from the former epithelial cells, and most likely are developed in an endomnous manner. The possibility can certainty not be denied, that they may have been produced independently and free in the interior of the seminal canals. But even in this latter case it is unquestionable that the vesicle in which they develope themselves is furnished by the epithelial cells and has formerly been contained in their lit terior. The difference even in this instance, therefore, would not be so very material, and might be reduced to a mere difference in the periods of formation. In both cases the seminal cc% might be assumed to be produced from the contents of the epithelial vesicles, either at a period when such contents are still contained in the interior of theni, or after they have become free.
Our preceding remarks respecting* the his tological relations of the seminal cells apply in an equal measure to all animals, and not merely to those the spermatozoa of which possess a linear form and are produced in the interior of the vesicles of developement. The Chilopoda, Acarina, Entomostraca, and Nematoda furnish us with sufficient proofs of this,—proofs- which contradict the as sumption of lalliker #, that a linear form of spermatozoa is common to all animals. Al though many of the differently-shaped seminal elements may, after a more accurate research, be proved to be mere forms of developement of the real spermatozoa, even this cannot be asserted with regard to all of them. These differently-shaped seminal elements are the very ones that here more particularly concern us ; we know that they differ in their develope ment from the ordinary seminal fibres. They Etre solid massive corpuscles, which, as we have already shown, have been produced simply and immediately from a metamorphosis of nuclei.