40 OPINIONS AND DISCOVERIES 



The liistory of sponges was in this state of uncertainty 

 when Dr R. E. Grant began those researches which shed 

 a new and clear light on their functions.* He first sa- 

 tisfied himself that the sponge is not the production of 

 any polypes, but, as Ellis had shown, an animal sui 

 generis, destitute of any sensible motion in its natu- 

 ral condition, and which cannot be made to evince 

 the slightest degree of contractility, under the strongest 

 irritations, either in its body as a whole, or in any part of 

 it, or even in the orifices. The sponge is a porous mass 

 permeated with canals which open on the surface by certain 

 orifices hitherto named the oscula, and the sm'face is be- 

 sides covered over with small pores or meshes. The in- 

 ner sm-face of the canals is " lined throughout their whole 

 winding and anastomosing covirse, with a smooth, soft, 

 glistening membrane," so firmly connected " mth the axis 

 or skeleton of the animal, that it could not possibly con- 

 tract 30 as to empty the whole of the internal canals, with- 

 out a general contraction of the entire sponge." And al- 

 though there is no contraction anywhere, yet the circum- 

 fluent water is seen to be absorbed by the small pores and 

 enter the body, whence it is again driven, in an even con- 

 tinuous current, through the canals and oscula, or, as they 

 should be called, \hQ fecal orifices, for they give exit to the 

 respired water, which flows out mixed also with opake fecu- 

 lent granules. Having put a small branch of the Spon- 

 gia coalita, with some sea-water, into a watch-glass, under 

 the microscope, Dr Grant says, — " on moving the watch- 

 glass, so as to bring one of the apertures on the side of 



* " Observations and Ex])eriments on the Structure and Functions 

 of the Sponge, by Robert Edinond Grant, M. D. &c." in tlie I3th and 

 14th vols, of the Edin. Phil. Journal. 



