40 OPINIONS AND DISCOVERIES 



the sponge, as well as its polypes, must be highly irritable, 

 and hence lends a willing ear to the statements of its sensi- 

 tiveness and contractility, which he even exaggerates : and 

 we are told not to wonder that the polypes remain undis- 

 covered, but to seek the explanation in the character of 

 their substance, which is a very transparent, hyaline and 

 colourless jelly filling the interstices of the sponge, while 

 the polypes, pullulating on the surface, are most minute. 

 And now, after tliis exposition, he exultingly exclaims, 

 all the observed facts relating to sponges easily explain 

 themselves, and fix beyond dispute our ideas on the origin 

 and nature of these bodies. We know that the sponge is 

 a soft, light, very porous, yellowish, greyish or whitish 

 body, which has the property of imbibing much water that 

 flows out again upon compression. Scattered over va- 

 rious species we observe holes of a considerable size (oscu- 

 la), which are not the cells of the polypes, but holes of 

 communication that furnish a common passage of issue to 

 several polypes, and by which the water reaches them. 

 Nevertheless certain excavations which we observe in the 

 sponge are the result of foreign bodies round which the 

 polypes are developed, or little hollows useful to the life 

 of the polypes which issue there.* 



The opinions of Professor Schweigger of Konigsberg, 

 who has paid especial attention to the family of sponges, 



Ton a confondus avec les alcyons, d'apres uneapparence exterieure; mais 

 je parle des vrais alcyons, c'est-a-dire, de ceux qui ont un polypier, le- 

 quel, dans sa structure, offre des fibres cornees, empatees d'une pulpe 

 qui se conserve et s'affermit dans son dessechement. Or ce sont ces 

 corps qui ont avec les Sponges des rapports que Ton ne saurait contester." 

 — Anim. s. Vert. ii. p. 348. 



* Histoire Naturelle des Animaux sans Vertebres, ii. p. 346-351. Paris, 

 1816. 



