45 



of the collared cells through the collars and into the cavity of 

 the chamber. Thus tlie question as to the coexistence or other- 

 wise of Sollas's membrane and the flagella of tlie collared cells 



is settled" In spite of the excellent preservation of my sec- 



tious I can fiud in Halichondria pauicea no apertures in Sollas's 

 membrane to allow of the passage of the water , and I am in- 

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

 merely as temporary and not definite openings, which is quite 



possible It appears almost certain that in some sponges 



Sollas's membrane completely stretches across the prosopyle, so 

 that the water has actually to pass through it on its way into 

 the chamber. We may compare the passage of the water through 

 Sollas's membrane to the passage of liqaids through organic mem- 

 branes by osmosis , only in sponges it is the flagella of the col- 

 lared cells which supply the necessary motive pov/er". The author 

 thinks it not likely that the membrane »always stretches com- 

 pletely across the prosopyles or inhalant apertures of the cham- 

 bers. Whether it does so or not probably depends upon the dia- 

 meter of the prosopyles. Thus in the Sycons , such as Grantia 

 labyrinthica, with large prosopyles, we may safely assume that 



the membrane ceases around the margin of the prosopyle 



Again , it is quite possible and even probable that temporary 

 gaps frequently make their appearance in the membrane , which 

 is , after all , only an extension of the delicate protoplasmic col- 

 lars of the collared cells , and it is well known how plastic and 

 chaugeable such structures are". 

 1891. Dendy, Arthur, A Monograph of the Victorian Sponges, 



Part. I. The Organisation and Classification of the Calca- 



rea Homocoela, with Descriptions of the Victorian Species. 



In: — Trans. R. Soc. Victoria. Vol. III. Part. lp, 1— 81 ; 



PI. I— XL Vide pp. 11 and 13. 

 The author describes the following peculiarity in Leucosolenia 

 tripodifera. 



ï>In the first place there is a well-developed Sollas's membrane 

 in the ordinary position, The flagella of the cells are retracted , 



