56 OPINIONS AND DISCOVERIES 



of Dr Grant's memoir,* when the pleasure of toying with 

 conjectiu-al indulgences was so far desti'oyed for ever. In 

 it he demonstrated that there was the closest resemblance 

 between the fluviatile and marine siliceous sponges, — a si- 

 milarity in structure associated with similar phenomena. 

 The fibrous net-work, — the siliceous spieula, — the gela- 

 tinous fluid with its granular bodies, — the pores of admis- 

 sion to the circiunfluent water, and the orifices for its expul- 

 sion, — its unintermitting current, unsoiled previous to its 

 circuit through the porous mass and loaded with feculent 

 matter on its issue, — and the general mode of growth, whe- 

 ther in the state of an ovum or in the adidt state, — were as- 

 certained to be essentially alike in both. But, adds Dr 

 Grant, " although in every respect a sponge, it (Spongilla) 

 has a more imperfect structure than any of the marine spe- 

 cies, wliich is observable in the sameness and feeble attach- 

 ment of the spieula, in the great size and defenceless state 

 of the pores and fecal orifices, in the general looseness of its 

 sm'face and internal texture, in the softness of its gelati- 

 nous matter, in the want of ciliae and spieula in its ova, — 

 indeed in every individual character." 



In consequence of his discoveries, Dr Grant, at a subse- 

 quent period, separated the sponges from other zoophytes, 

 and formed with them a distinct order mider the title of 

 " Poriphera." It is considered inferior to the Polypes in 

 the system, but superior to the polygastric or infusory ani- 

 malcules, f 



* " On the structure and nature of the Spongilla friabilis," in Edin. 

 Phil. Journ. xiv. p. 270—284. 



t Outlines of Comp. Anatomy, p. 5. There is an excellent sum- 

 mary of Grant's discoveries by Milne-Edwards in Lam. Anim. s. Vert. 

 2tlc edit, ii. p. d'-io. 



