MATERIALS FOR A MONOGRAPH OF THE ASCONS. 527 



they are absorbed more or less rapidly as the spicule grows, in 

 the case of the gastral actinoblasts they persist throughout in 

 undiminished size and quantity. As I am not acquainted with 

 any species with quadriradiates which shows colour varieties^ I 

 am unable to state whether the granules in the gastral actino- 

 blasts would retain the vivid coloration which the granules 

 often show in some species, — coriacea^ for instance. In the 

 latter I have seen an orange-red specimen which had a sieve 

 membrane across the osculum, and, as might have been ex- 

 pected, the sieve membrane was also of an orange-red colour. 



I am not able at present to make any positive statements 

 about these granules, but will briefly notice some views that 

 have been put forward about them. 



Bidder (1892 and elsewhere) regards the granules as excre- 

 tory, especially in the porocytes. They seem, however, too 

 constant an element in the cells of the dermal layer for 

 Bidder's theory to be a complete explanation of them. There 

 is, moreover, a strong prima facie argument against the cells 

 of the flat epithelium or the porocytes being concerned in 

 excretion, as then the excreted products would immediately be 

 carried back into the sponge by the currents. On the other 

 hand, it must be confessed that the porocytes which line the 

 oscular rim would be in a particularly favorable situation for 

 exercising the function of excretion. 



Topsent, on the other hand, as we have seen, regarded the 

 granules of the porocytes, or " cellules spheruleuses/' as repre- 

 senting reserve nutriment. It might be doubted if Topsent 

 would have come to this conclusion had he known that the 

 " cellules spheruleuses " were simply contracted pore cells. 

 He seems, further, to have overlooked the fact that similar 

 granules occur in the cells of the flat epithelium. 



It seems to me probable that the granules in question sub- 

 serve more than one function, but as a peculiarity of all the 

 cells in which they occur is their contractility, especially in 

 the case of the porocytes in which they are most abundant, I 

 have long thought they might have some connection with this 

 function. Biitschli has shown how, on the alveolar theory of 



