RADIAT A . EChinOderMaia. The sper matozoa, in the division of the Echi nodermata, possess, it seems throdghout, a pin-like form (fig. 393.), with a small Gordius appear in the shape of short rods without any corpuscles.
We cannot doubt that these seminal ele ments are developed spermatozoa, having sought in vain, and for a long time, for other forms of developement, and having found roundish body (of wi--6"/), and a very slender tail appendix of about -11-6"'--516-"'. It is only in rare cases (as Spatangus) that the body, has an oblong form, and is rather pointed at the anterior end.
The developing cells of these spermatozoa are very small, and lie in groups, as in the Bryozoa,,inclosed in large cyst-like mother cells. The developement of the spermatozoa undoubtedly takes place according to the usual mode, although it cannot be proved with certainty, and although the appearance seems rather to indicate a gradual elonga tion of the cells. The spermatozoa lie to gether in bundles, either enclosed by the cysts or free.
Acalephie and Anthozoa. The Acalephae and Anthozoa exhibit quite a similar series ofphe nomena. The bodies of the spermatozoa are usually round, frequently however, especially among the Medusre ( fig. 391.), oblong, cy lindroid. Little is as yet known respecting their developcnient. The spermatozoa have generally a fasciculated style of grouping together, and mostly so at a period when they are still enclosed by cyst-like cells. Pre vious to the maturity of the generative capa city, these cysts contain, as has been proved with regard to the Medusw, numerous small vesicles, which subsequently pass through ap parent prolongation into spermatozoa.
Infusoria. The Infusoria are especially distinguished by the want of a sexual mode of propagation. There is no trace of either spermatozoa or ova to be discovered in them. Ehrenberg, it is true, describes in these animals particular organs of procreation, both male and female ; but there is no foundation for the assignment of such an import to these particular parts of their structure, it being altogether an arbitrary one. The proof of the existence of spermatozoa and ova the ' characteristic structures is indis pensably necessary to prove the embryo-pre paring function of certain parts, and to justify their being interpreted as generative organs.
General conclusions respecting the nzorphology and developenzent of the spernzatozoa. A re view of the description now lying before us, of the forin and developement of the seminal ele ments in the several divisions of the animal kingdom, and of the mutual relations of the respective formations, must unavoidably lead us to claim for them a different morphological value.
By far the greater part of the spermatozoa, all the so-called seminal fibres, which are distinguished by the linear form of the body, are produced in an endogenous way, and that (with the exception of the spermatozoa in the Decapoda) separately in the interior of vesicular elements. IC:Weer* was the first who directed attention to the wide exten sion of this mode of production hav ing claimed it likewise for such animals, in which appearances are rather in favour of an immediate metamorphosis of the vesicles of developement into seminal fibres (by means of elongation, growing out, Bcc.). The lays s of amlogy certainly justify us in drawing the same inference as Kiilliker ; the more so, as observation has proved that many animals, the developement of whose spermatozoa was formerly accounted for by the latter me thods, evidently also follow the endogenous type.
It is difficult to trace the intimate develope ment of the spermatozoa in the interior of these vesicles ; but it appears probable that it is brought about by the junction of molecular corpuscles, which join each other linearly, and uhich have been deposited from the con tents of the vesicles. Indeed, such a mode of procedure does not seem to be at all sin gular in the history of' developement of organic tissues. By saying this, we do not exactly mean to allude to the mode of formation of the muscular fibrils in the interior of the sarcolemma of a so-called primitive fasciculus, since at present we know too little about it ; yet, we cannot help reminding our readers of the process of lignification in the vegetable world, or of the production of the so-called spiral vessels, which essentially seem to be founded on a perfectly analogous deposit of a firm substance, from that which was at first fluid.