Mr. H. J. Carter on Zoos-perms in Spongilla. 335 



On further examination, the cell appeared to be formed exactly 

 like the sponge-cell itself, but proportionally minute in every 

 respect — that is, that granular matter, interspersed with a few 

 granules of much larger size, is spread over more or less of the 

 internal surface of the cell, giving it the appearance at one time 

 of being entirely granular and at another of being only partially 

 so, according as the granular matter is wholly or partially upper- 

 most (figs. 1, 2). Moreover, the cell frequently changes its 

 shape, which shows that, like the sponge-cell, it is also meta- 

 morphic (figs. 3, 4, 5). One hair-like appendage only projects 

 from its surface, which, in length, is about three times the dia- 

 meter of the cell, and occasionally appears to widen at the base, 

 as if it were a prolongation of the cell-wall itself; its motions 

 might be likened to those of a rope, so shaken at one end that 

 the undulations extend throughout, and therefore when used in 

 progression this filament gives to the cell a " serpentine creep- 

 ing" course. 



At first the polymorphism of the cell and movements of the 

 tail are so rapid, that literally, neither " head nor tail " can be 

 made out of the little mass. Presently, however, its power of 

 progression and motion begins to fail, and if separated from 

 other fragments it soon becomes stationary, and after a little 

 polymorphism assumes its natural, passive form, which is that 

 of a spherical cell (fig. 1). During this time the motions of 

 the tail become more and more languid and at length cease 

 altogether. 



If, on the other hand, there be very large fragments in the 

 immediate neighbourhood, or an active sponge-cell Tinder poly- 

 morphism sweeps over the field, it may attach itself to one or 

 the other of these, when its cell becomes undistinguishable from 

 the common mass, and the tail, floating and undulating out- 

 wards, is all that remains visible. Hence many of the larger 

 fragments present more or less of these filaments on their cir- 

 cumference (fig. 6). 



To see if any existed on the investing membrane of the sur- 

 face, or on the lining membrane of the canals of Spongilla, a 

 slice including portions of both was placed under the micro- 

 scopic power mentioned, but none presented themselves, neither 

 was there any motion in the surrounding particles indicative of 

 the presence of cilia. 



This cell, which is by far the most active in its movements of 

 any part of Spongilla, makes the whole of the fragments tremble, 

 when a portion of the latter is first torn to pieces, after the man- 

 ner of the swarming, vibrating movements observed in the sperm- 

 cells of mosses, when the fully-developed mass just quits the 

 antheridium. They are about the 1 -4300th part of an inch in 



