igoy.] Records of the Indian Museum. 271 



do not differ from the other epithehal cells of the membrane except 

 that they are often slightly attenuated in a horizontal plane. 



Outline ot a small portion of the external surface of the dermal membrane of 

 S. proliferens. showing flattened epithelial cells {e c.) and pores (/>.), x about irgo. 

 The membrane was taken from the edge of the sponge and stained with haematoxylin. 

 The outline was drawn with a camera liicida and slightly enlarged. «. = nuclei; pc.= 

 pore cell 



In the majority of Spong''llcB that occur in Calcutta, however^ 

 the pores can only be detected with the aid of a fairly high power 

 of the microscope and open not directly into the termination of the 

 afferent canals but into the subdermal space, their exact arrange- 

 ment differing in different species. In such forms the subdermal 

 space is often ver^^ large. Sponges which have this form of pore 

 differ widely in other respects ; those with which I am best ac- 

 quainted are 5. crassissima and S. proliferens. In such forms the 

 pore is as a rule surrounded by a single cell. The actual hole is 

 almost circular ; the cell that surrounds it has a minutely granular 

 cytoplasm and a small nucleus that stains very deeply. For the 

 greater part of its circumference the cell is attenuated to a mere 

 filament ; at the point at which the nucleus is situated it swells 

 out considerably in both planes, while it is most attenuated at the 

 opposite extremity. In all cases, so far as my observations go, the 

 cell completely surrounds the pore, if onh^ one cell is present, 

 without a sign of secondary fusion at any point ; but the relative 

 proportions of the cell and the pore differ considerably and in some 

 cases the latter is nearh^ in the centre of the former. Without 

 further information it would be impossible to escape from the 

 conclusion that the pore was intracellular ; but even were this the 

 case, it would not be necessary to assume that the porocyte was 

 homologous with that of the Calcarea. Indeed, there is one im- 

 portant difference, viz., the pore-surrounding cell in Spongilla is 

 not contractile, and cannot close the pore. In some cases, more- 

 over — in 5. crassissima at any rate— the pore is not surrounded by 

 one such cell, but by two. In such cases each cell is bent into a 

 semi-circle, having a crescentic outline, and the two adhere together 



