MATERIALS FOH A MONOGRAPH OF THE ASCONS. 485 



by the body of oue such cell. At oue side of the pore is 

 lodged the nucleus iu a thickeuiug of the wall of the pore. 

 Sometimes the protoplasm surrounding the nucleus is clear, 

 but more often it is so full of granules as to obscure the view 

 of the nucleus (figs. 18, 19, 39). In its position the nucleus 

 is usually situated rather towards the gastral aperture, nearly 

 on a level with the collar-cells. 



The minuter characters of the pore-cells are such as to 

 leave but little doubt, even if there were no further evidence 

 obtainable, as to their histological affinities. In all respects 

 the pore-cells resemble the cells of the flat epithelium, but 

 with the characters of the latter exaggerated. The nucleus 

 is similar in structure, but slightly larger, and usually paler in 

 its staining reactions (osmic and picrocarmine). The granules 

 are identical in character with those of the epithelium, but 

 are present in much greater number — the cell, as a whole, 

 being much bigger, — and attain, both on the average and 

 in individual instances, a much greater size. This is less 

 noticeable in coriacea, with its very granular epithelium, 

 than in such a species as con tort a, where the epithelial 

 cells have fewer and smaller granules (compare PI. 41, 

 figs. 39 and 40). In consequence of the great increase 

 in the size and number of the granules, the yellowish- 

 brown colour which they impart to the cells in osmic-picro- 

 carmine-glycerine preparations is very distinct, and picks 

 them out at once from the rest of the tissue elements, even 

 in those species in which this tint is scarcely discernible in 

 the epithelial cells. In life also the granules of the pore-cells 

 show the peculiarities described above for the epithelial cells, 

 being dull white when the sponge is white, and of the same 

 colour as the sponge when it is coloured. In short, apart 

 from the especial functions and consequent peculiar form of 

 the pore-cells, or porocytes. as they may be termed gene- 

 rally, we may say that while, on the one hand, all their 

 characters show them to belong to the same category as the 

 epithelial cells, on the other hand, those characters are modi- 

 fied to an extent and with a constancy sufficient to enable us 



VOL. 40, PART 4. NKW BEK. M M 



