ivith some Remarks on the Nature of the Spongiee Marinse. 383 



These gemmules with their numerous cilia may be seen, on referring to the 

 drawings that accompany Dr. Furre's paper, in Phil. Trans., plate 26, at figs. 

 20 — 23, where they are delineated on an enlarged scale 



Dr. Grant has likewise published some observations on tiie spontaneous 

 motions of the ova of several Zoophytes, well worth perusal, in tlie Edinb. 

 New Phil. Journ. for 1826, at p. 150 and the following pages*. 



Now, by comparing these descriptions with those before given of the germs 

 or sporules of Ectosperma, and of tlie germlike bodies both of the SpougiUa 

 and of tlie Spoug'uv, it will be evident that these gemmules possess far more 

 vigorous and rapid powers of locomotion, arising doubtless from their finlike 

 cilia, and their actions exhibit more volition or a greater degree of spontaneity, 

 and precisely that which usually pertains to animal life : wherefore, they more 

 nearly resemble in those powers the Infusorian Volvox. It likewise appears 

 from those authors, as well as from the earlier accounts of Cavolini, that the 

 genmiules of Zoophytes frequently change their forms in swimming, that 

 they have considerable powers of contraction and dilatation of tlieir whole 

 bodies, and are otherwise liighly irritable ; hence, in these characters they 

 present an essential difference both from the sporules of the River Sponge, and 

 from the germlike bodies of the Sea Spongesf : but these gennnules, in respect 

 to their irritability alone, much nearer approach the In/itsoria ; and thereby, 

 I think, their animal nature is sufficiently established. Also we know from 

 Dr. Unger's very conclusive experiments, that the locomotive sporules of the 

 Ectosperma are those of a true plant ; and since the moving germlike bodies 

 of both kinds of Sponge are much more analogous in every respect to those, 



* And for that author's account of the ova of Flustrce, see the same Journal for 1827, p. 116. I 

 must however object to the term ova (eggs) being used to designate the reproductive bodies (gem- 

 mules) of Zoophytes : because, these being enveloped by a mere skin or membrane, usually furnished 

 with cilia, endowed with irritability or powers of contraction and dilatation, and frequently, if not al- 

 ways, possessed of some kind of muscular apparatus, are rendered totally distinct from any ova or 

 ovula, i. e. such reproductive bodies as are simply inclosed within unorganized coverings or plain ex- 

 ternal shells. Although Dr. Allan Thomson incorrectly considers the distinction between eggs and 

 gemmules to be somewhat arbitrary. Vide note at p. 46 of Johnston's Brit. Zooph. 



t Dr. Grant positively asserts the ova of the Sea Sponges " do not change their forms while 

 swimming,' (p. 154, loc. cit.) And I have not witnessed either any such changes, or any symptoms 

 of irritability, in the sporules of the River Sponge. 

 VOL. XVIII. 3 E 



