28 PROTOZOA. 



another manner, which is the ordinary mode of their reproduction, and 

 forms a very interesting portion of their history*. At certain seasons 

 of the year, if a living sponge be cut to pieces, the channels in its 

 interior are found to have their walls studded with yellowish gelatinous 

 granules, developed in the parenchymatous tissue ; these granules arc 

 the germs or gemmules from which a future race will spring ; they seem 

 to be formed indifferently in all parts of the mass, sprouting, as it were, 

 from the albuminous crust that coats the skeleton, without the appear- 

 ance of any organs specially appropriated to their development. As 

 they increase in size, they are found to project more and more into the 

 canals ramifying through the sponge, and to be provided with an appa- 

 ratus of locomotion of a description such as we shall frequently have 

 occasion to mention. The gemmule assumes an ovoid form (fig. 10, B), 

 and a large portion of its surface becomes covered with innumerable 

 vibrating hairs, or cilia, as they are denominated ; these are of incon- 

 ceivable minuteness, yet individually capable of exercising rapid move- 

 ments, whereby they produce currents in the surrounding fluid. As 

 soon therefore as a gemmule is sufficiently mature, it becomes detached 

 from the nidus where it was formed, and being whirled along by the 

 issuing streams, is expelled through the fecal orifices of the parent, and 

 escapes into the water around. Instead, however, of falling to the 

 bottom, as so apparently helpless a particle of jelly might be expected 

 to do, the ceaseless vibration of the cilia upon its surface propels it 

 rapidly along, until, being removed to a considerable distance from its 



to ciliated epithelium-cells is rendered abundantly manifest by the revelations of 

 the microscope to modern observers 1 . From these researches it would appear 

 that the origin of the Spermatozoa is invariably to be traced to nucleated cells, in 

 the interior of which they are individually developed. These developing-cells, or 

 vesicles, as they ave termed, are found at certain seasons crowding the seminiferous 

 tubes of the testes in immense numbers. Taken from the body after death they are 

 seen to be perfectly transparent and filled with a fluid which on coagulating becomes 

 somewhat granular. Most of these developing-cells (fig. 13, a, b, c} are found freely 

 floating in the minute seminal canals, but frequently they are enclosed in another 

 cell-like envelope, either singly (d) or in numbers of three, four, six, or seven in 

 each; the existence, however, of a more considerable number (e, /) in one common 

 cyst is unusual. Whether single or more numerous, however, it is in the developing- 

 cells that the Spermatozoa are formed by a kind of endogenous growth, at first 

 appearing like dim shadows lying amongst the contained granules, but gradually 

 assuming a sharper outline as the body and, subsequently, the tail are perfected. 

 The entire Spermatozoon at length becomes visible coiled up in the interior of the 

 cell, which, when the development is completed, bursts and discharges its contents. 

 * Professor Grant. 



i Vide Von Siebold, in Miiller's Archiv, 1836 and 1837: E.Wagner, Fragment e 

 zur Physiologic der Zeugung ; Beitriige zur Geschichte der Zeugung und Entwicke- 

 lung, in den Abhandlung. der Konigl. Bayerisch. Akad., Munich, 1837 : Kolliker, 

 Beitrage zur Kenntniss der Geschlectsverhaltnisse und Samenfliissigkeit wirbellosen 

 Thiere, Berlin, 1841 ; Die Bildung der Samenfaden in Bliischen, Nuremberg, 1840. 



