46 



but the collars are in some cases well preserved and funnel-shaped. 

 Their margins do not come into direct contact, but are united 

 by the membrane, which runs from one to another at right 

 angles to the long axes of the collars. In vertical sections this 

 membrane appears as a thin , sharp line running parallel to the 

 row of collared cells, and at a little distance (about the length 



of a collared cell body) from it Not only , however , is 



Sollas's membrane present, but it presents in itself a very pecu- 

 liar modification. Instead of being perfectly smooth the outer 

 surface is thickly studded with delicate , rod-like processes of 

 uniform length and projecting at right angles from it into the 

 gastral cavity". It is suggested that if Bidder's and author's 

 hypothesis that Sollas's membrane serves to catch or filter food 

 particles, is maintained , »it seems possible that the curious rod- 

 like processes .... may be a further device for the same purpose". 

 1892. Bidder, George. Note on Excretion in Sponges. In: — Proc. 

 R. Soc. London. Vol. LI p. 474—484. Vide pp. 478 and 479. 



»In Heterocoela (probably it is similar in Silicea) the collars 

 of the collar cells are at first mere fringes, which help to retain 

 the food and filter the water as it passes from the base of the 

 cell to the moving tip of the flagellum. When the cell is satia- 

 ted the flagellum cesses to move , and degenerates ; the collar 

 unites with the neighbouring collars to prevent the water that 

 is already filtered and already foul from returning past the in- 

 active area to pollute the afierent water supply. When the food 

 has been digested, the cells elongate and become closely pressed 

 together, the separation of their distal parts start on a new cycle 

 with hungry protoplasm, active flagella, and separated collars. 



In the Homocoela I have been unable to make sure of these 

 changes other than as regards the habitual association of Sollas's 

 membrane with the absence of flagella, and of the presence of 

 flagella with separated collars". 



1892. Delage, Yves. Embryogénie des Eponges. In : — Arch. Zool. 

 Expérim. (2) Tomé X p. 345—498. PI. XIV— XXI. Vide 

 pp. 364, 365 & 447. 



