42 



Worms iri 

 them 



adventitious. 



Texture of 

 sponges differ- 

 ent. 



Distinction be- 

 tween alcyonia 

 and sponges. 



FOSSIl ALCYONIA. 



sea, a systolic and diastolic motion, in certain little round 

 holes, which lasted until the water they had contained was 

 quite dissipated. Mons. Peysonell supposed sponges to 

 have been formed by certain worms, which inhabited the 

 labyrinthean windings of the sponge ; and believed, that 

 whatever life was found in these substances, existed in these 

 worms, and not in the substance of the sponge, which he 

 was convinced, was an inanimate body. This point was, 

 however, determined by Mr. Ellis, who, in a letter to 

 Dr. Solander*, relates the observations which he had made; 

 by which he ascertained, that these worms, which he found 

 in the sponge in great numbers, were a very small kind of 

 nereis, or sea scolopendra ; and that they were not the fa- 

 bricators of the sponge, but had pierced their way into its 

 soft substance, and made it only their place of retreat and 

 security. Upon examining, in sea water, a variety of the 

 crumb of bread sponge, the tops of which were full of tu» 

 bular cavities or papillae, he could plainly observe these 

 little tubes to receive and pass the water to and fro ; so that 

 he inferred, that the sponge is an animal sui generis, whose 

 mouths are so many holes or ends of branched tubes, 

 opening, on its surface ; with these, he supposes, it re- 

 ceives its nourishment, and discharges, like the polypes, its 

 excrements. 



Mr. Ellis also discovered, that the texture is very dif- 

 ferent in different species of sponge : some being composed 

 wholly of interwoven reticulated fibres, whilft others are com- 

 posed of little masses of ftraight fibres of different sizesf 

 from the moft minute spiculae to ftrong elastic shining; 

 spines, like small needles of one third of an inch long ; 

 beside these, he observes, there is an intermediate sort, 

 between the reticulated and the finer fasciculated kinds, 

 which seem to partake of both sorts. 



In the substances considered as alcyonia by Donati, as 

 well as in some of those which have been described by 

 Count Marsilli, similar large bundles of elastic fibres like 

 needles were difcovered. Thefe had been reckoned alcyonia 

 by moft authors, but in Mr. Ellis's opinion they mould not 



Phil. Trans, vol. LV. p. 280, 



be 



