68 Proceedings of the Royal Society of Victoria. 



been able to demonstrate the existence of this connecting 

 membi-ane, which for the sake of convenience we may 

 terra Sollas's membrane, in the flagellated chambers of 

 Stelof^pongus. 



The collared cells are arranged at about equal distances 

 all around the chamber, but they are interrupted at the 

 proximal pole by the inhalant aperture, and at the distal pole 

 by the exlialant aperture. They are not all of the same 

 size, but largest around the inhalant aperture, and gradually 

 diminishing towards the exhalant aperture, around which 

 they are smallest. Each cell consists of a cylindrical collum 

 or neck with a large nucleus lying in its slightly expanded 

 base (the body of the cell). The collum projects into the 

 chamber, and gives support to the delicate membranous 

 collar, which is rather longer than the collum, and 

 considerably wider at its summit. Thus the whole cell, 

 including the collar, has somewhat the shape of a dice-box, 

 being narrower in the middle than at the two ends. I have 

 not been able to trace any definite outline to the body of the 

 cell, which is imbedded in a highly granular ground 

 substance, but the nuclei are always very conspicuous. The 

 flagella cannot be detected in my ]>reparations, being entirely 

 shrivelled up, or possibly retracted when the sponge was 

 placed in spirit. 



The margins of the collars are all connected together by a 

 continuous delicate membrane (Sollas's membrane), which lies 

 in a plane at right angles to the long axis of the collared 

 cell. This membrane is seen in thin vertical sections as a 

 fine thread running from collar to collar. If, however, the 

 .sections be taken in a plane more or less parallel to Sollas's 

 membrane, then the latter frequently appears as an irregular 

 network of delicate transparent strands, shiivelled up and 

 distoi'ted by the action of reagents, but easily recognisable 

 lying within the chamber. 



From what has been said of the sizes and arrangement 

 of the collared cells in each chamber, it will be seen that the 

 membrane joining their margins will not run parallel to the 

 wall of the chamber, but will be furthest from it at the 

 proximal or inhalant pole, and nearest to it at the distal or 

 exhalant pole. At the proximal pole, in fact, the membrane 

 is widely separated from the wall of the chamber, while at 

 the distal pole, the two became confluent. Hence the 

 mem brane has the form of a cup, whose concavity is turned 

 towards the exhalant aperture of the chamber. 



