with some Remarks on the Nature of the Spongiae Marinae. 383 



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

 drawings that accompany Dr. Farre'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 the spontaneous 

 motions of the ova of several Zoophytes, well worth perusal, in the 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 the germlike bodies both of the Spongilla 

 and of the Spongice, 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 moi-e volition or a greater degree of spontaneity, 

 and precisely that which usually pertains to animal life : wherefore, they moi'e 

 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 

 gemmules of Zoophytes frequently change their forms in swimming, that 

 they have considerable powers of contraction and dilatation of their whole 

 bodies, and are otherwise highly 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 Sponges f : but these gemmules, in respect 

 to their irritability alone, much nearer approach the Infusoria ; and thereby, 

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

 Dr. Lingers 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 Flustra, 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 



