OF THE SPONGIAD^. Ill 



higher classes of animals. In some cases, as in Geodia 

 M'Andrewii and Barretti, Bowerbank, MS., we find the 

 pores systematically congregated in groups, as in Fig. 302, 

 Plate XIX, which represents two groups from the latter 

 species, and this congregation is accounted for by the 

 peculiarities of the form and arrangement of the inter- 

 marginal cavities of that class of sponges. 



In my "Further Report on the VitaHty of the Spongiadae," 

 published in the 'Reportsof theBritish Association' for 1857, 

 I have described at length the opening and closing of the 

 pores in Spongilla jluviatilis ; each operation is commenced 

 and terminated in less than a minute ; they are perfectly 

 dependent on the will of the animal, and in neither case are 

 they simultaneous, but follow in irregular succession, in 

 accordance with the necessities of the animal ; and when 

 once closed, they do not appear to ever open again in pre- 

 cisely the same spot. 



In these wonderful opening and closing operations in the 

 dermal membrane of Spongilla, every movement is accom- 

 plished as systematically and accurately as if there was a 

 perfect system of nerves and muscles present, while not a 

 vestige of fibrous structure can be detected in the thin 

 translucent membrane and its sarcodous lining. No 

 cicatrix remains for an instant after closing, no indication 

 of the spot where the opening is the next moment to be 

 effected. 



In sponges exposed to the action of the atmosphere, 

 between high- and low-water marks, and in dried speci- 

 mens, the pores can rarely be detected. In the first case 

 they are carefully closed on the receding of the tide, that 

 the water within them may be safely retained during their 

 exposure to the atmosphere, and in the latter case the 

 violence offered to it, and the shock of its removal from its 

 native locality, is sufficient to induce an immediate closing 

 of those organs, as I have shown in the details of my 

 observations on these organs in Spongilla in the volume of 

 the ' Reports of the British Association' for 1857, to which 

 I have before alluded. But should a specimen of marine 

 sponge, after a careful removal from its place of growth, be 



