STUDIES ON THE COMPARATIVE ANATOMY OF SPONGES. 343 
the chamber, since its convex surface is always turned towards 
the prosopyle/’ 1 
This short passage, and a not very satisfactory woodcut accom- 
panying it, comprise all the information which we as yet possess 
concerning this very remarkable and important structure, but 
doubtless further details will be given in Professor Sollas's 
forthcoming report on the “ Challenger/’ Tetractinellid a. 
Meantime it has been my good fortune to be able to demon- 
strate, beyond the possibility of a doubt, the existence of this 
connecting membrane, which I propose to call Sollas’s mem- 
brane, in Stelospongus. 
In Stelospongus the collared cells are arranged at about 
equal distances all around the flagellated chamber, but they 
are interrupted at the proximal pole by the inhalant, and at 
the distal pole by the exhalant aperture (figs. 6, 10). They are 
not all of the same size ; they are largest around the inha- 
lant aperture, gradually diminishing towards the exhalant 
aperture, around which they are smallest (figs. 6, 10). Each 
cell (figs. 8, 9) consists of a cylindrical “ collum ” or neck, 
with a large oval nucleus lying in its slightly expanded base 
(the body of the cell). The collum projects freely into the 
chamber, and gives support to the delicate membranous collar. 
The collar is rather longer than the collum, and, though 
necessarily of the same diameter as the latter at its base, 
considerably wider at its summit. Thus, the whole cell, in- 
cluding 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 embedded in the highly granular ground sub- 
stance, but the nuclei are always very conspicuous as relatively 
large, deeply-staining, oval, granular bodies, sometimes appa- 
rently with a nucleolus (fig. 8). 
The flagella cannot be detected in my preparations, being 
entirely shrivelled up, or possibly retracted, when the Sponge 
was placed in spirit. Certain granular bodies, sometimes visible 
on the collars and represented in fig. 8 (g.), may possibly 
1 = inhalant aperture. 
