39 



II. Opinions of otlier authors. 



1888. Sollas, W. J., [Article] Spouges. lu : — Encyclopaedia 



Britannica. Ed. IX. Vide p. 418. 



»In Tetractiuellida , and probably in many other sponges — cer- 



taiuly in some — the collars of contiguous choanocytes coalesce 



at their margins so as to produce a fenestrated membrane, which 



forms a second inner lining to the flagellated chamber". 



1888. Sollas, W. J., Report on the Tetractinellida. In: — Report 



OU the Scieutific Results of the Voyage of H. M. S. Chal- 



lenger Zoology. Vol. XXV. p. I— CLXVI and 1— 



458. PI. I— XLTV. Vide pp. XXXVI, XXXVII and Cl. 



The author further states that »distally the collar curves out- 



ïvards and beeomes concrescent with the similar collars of the 



surrounding choanocytes. From the concrescence of the collars 



there results a delicate film or membrane Looked at face 



on this membrane has the appearance of being fenestrated by 

 regularly distributed round or oval openings, which represent 

 the openings of the tubular collars of the choanocytes. Sometim es 

 a small cell with a distinct nucleus is present in the lumen of 

 one of these fenestrae; this appears to belong to one of the 

 choanocytes , which has been torn from its attachment to the 

 chamber-wall and pulled by the contraction of the collar to a 

 level of the membrane. The physiological meaning of this struc- 

 ture is not obvious; that it is not an artificial product appears 

 from the constancy with which it is present in certain groups 

 and not in others; I have never seen more than doubtful signs 

 of it in the Monaxonids , it certainly does not occur in the Sub- 

 eritidae nor in the Tethyidae , and it may possibly prove to be 

 characteristic of the Tetractinellida only. 



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 succeeded in fiuding any; it is possible 

 that the apertures have the form of pores uo larger than the 



