Extracts from the Mlnute-Book of the Linnean Society. 503 



of the Ectosperma. This resorption or disappearance of the cilia 

 after a certain period will readily account for the denial of their ex- 

 istence by practised microscopical observers. 



The existence of cilia subservient to locomotion is far from deter- 

 mining, in Mr. Hogg's opinion, the question of the animal nature of 

 the bodies to which they belong, although the zoocarpical theory, 

 which he regards as most improbable, appears to be still gaining 

 ground. He thinks the motive power of the cilia of the sporules 

 of Spongilla and the Algce, as also of the Sea-Sponges, to be depen- 

 dent on some peculiar organization not connected (as in the loco- 

 motive gemmules of a zoophyte) with any muscular apparatus; un- 

 less indeed, as he has before suggested, mere endosmosis and exos- 

 mosis should be found sufficient to produce it. 



Mr. Hogg refers to the very great similarity between the loco- 

 motive sporules of Ectosperma as figured by M. Thuret, of Spongilla 

 as given by M. Laurent, and o( Spongia as represented by Dr. Grant. 

 The granular epispore to which the cilia are attached, described and 

 figured by M. Thuret as investing the sporule of Ectosperma, is per- 

 ceptible in M. Laurent's figure of that of Spongilla, and plainly seen 

 in Dr. Grant's of Spongia ; and it evidently differs from the covering 

 (epigemmule) of the locomotive gemmule of a zoophyte. No men- 

 tion is made by M. Laurent of the papillae discovered by Mr. Hogg, 

 with a magnifying power of above 400, on the external covering of 

 the locomotive sporules of Spongilla, and described by him at p. 378 

 of the previous volume ; but Mr. Hogg believes that if the sporule 

 figured by M. Laurent (at pi. 1. fig. G. 1 a.) had been more highly 

 magnified, the exceedingly minute granulations just visible near the 

 extreme edge of that figure would have proved to be these granular 

 papillae. He also adverts to the argument derived by M. Laurent in 

 favour of the animal nature of Spongilla, from its scissiparous re- 

 production, anol compares this process with the observations of M. 

 Thuret on the scissiparous division of Ectosperma, with the view of 

 showing that there is a more perfect analogy with the latter, and 

 consequently with Algce, than with Hydra and other Polypes. 



voir. XIX. 3 u 



