STQDIES ON THE COMPARATIVE ANATOMY OF SPONGES. 45 



1, b). This fact has also been observed by Sollas in the case 

 of the Tetractinellida (op. cit.), and is well shown in his 

 diagram of the protoplasmic continuity of a sponge. I have 

 also seen and figured at x. in fig. 1 what appears to be a con- 

 nection of a collared cell with a stellate cell in the surrounding 

 mesoderm^ as described by Sollas. 



We have now to face the difficult question^ " How does the 

 water from the inhalant lacunae enter the flagellated chambers?" 

 Sollas (op. cit.) observes, '' Since the fenestrated membrane 

 stretches across the flagellated chamber transversely there 

 must be an aperture or apertures in it for the passage of water 

 from the prosodus to the aphodus, though I have never suc- 

 ceeded in finding any ; it is possible that the apertures have 

 the form of pores no larger than the lumen of the choanocytal 

 collars, and in this case they would be very difficult to dis- 

 tinguish." 



In spite of the excellent preservation of my sections I can 

 find in Halichondria panicea no apertures in Sollas^s mem- 

 brane to allow of the passage of the water, and I am inclined 

 to believe that either there are none, or that they exist merely 

 as temporary and not definite openings, which is quite possible. 

 The idea that there are no openings may seem at first sight 

 rather strange, but I believe it to be quite reasonable, if not 

 probable. 



After having arrived at this point in the present paper I at 

 length obtained access to Bidder's " Note on the Physiology of 

 Sponges," ^ which I had hitherto been unable to see. I find 

 that this author has forestalled me in a suggestion which I was 

 about to make concerning the function of Sollas^s membrane, 

 namely, that it serves to filter food particles from the current 

 of water flowing through the sponge. As the note in question 

 is very brief I may perhaps be allowed to quote it in full. 



"After feeding with suspended carmine a calcareous sponge 

 (Leucandra aspera, Vosmaer) the author found that in it 

 the carmine was at no time in any but the collared cells. The 



^ 'Proceedings of the Cambridge Philosophical Society,' vol. vi, part 4 

 p. 183. 



