MATEEIALS FOR A MONOGRAPH OF THE ASCONS. 483 



lated, and the granules^ which are small, are lodged at the 

 nodes, giving the cells a characteristic marbled appearance, 

 with a yellowish-brown tint, rather more brownish than in the 

 other species. The epithelial cells of reticulum are very 

 similar to those of cerebrum, except that the granules are 

 larger and the vacuolation less marked, giving a more normal 

 appearance. 



Finally I have examined at Banyuls a species apparently 

 new, with all three kinds of spicules, triradiate, quadriradiate, 

 and monaxon. I propose to refer to this species as Clathrina, 

 sp. dub., in the present memoir. The epithelial cells of this 

 species are very similar in their characters to those of 

 coriacea, but rather less granular (PI. 39, figs. 17 — 20). 



Thus the dermal epithelium shows not inconsiderable varia- 

 tions in its general appearance in different species, but in all 

 the forms its main characteristics are similar — flattened 

 granular cells of a type easily recognised. One small point 

 remains for notice, as it may at first sight seem strange in the 

 figures. The flat epithelium forms the external covering of 

 the dermal layer, and the spicules are placed of course inter- 

 nally to it, lodged in the structureless jelly which makes up 

 the greater part of the dermal layer. In some species, where 

 the wall contains a great number of large spicules, those 

 placed more externally often cause the wall to bulge out to 

 such an extent that the spicules sometimes become almost 

 enveloped in the epithelium, which is seen to be tucked in 

 under them. Thus in PI. 39, fig. 19, a surface view of Clath- 

 rina, sp. dub., from the inner or gastral side, the cells of 

 flat epithelium often appear on the upper side of the spicules 

 placed most deeply, although, being external, they should 

 really appear below all the spicules. Other epithelial cells 

 are seen here and there in side view. Similarly in fig. 20, 

 seen from the dermal aspect, some of the epithelial cells 

 appear almost hidden under the spicules. These appearances 

 are not difficult to understand, and need not detain us further. 



The Pores. — The true nature of the pores was first 

 described by Bidder (1891, p. 631) and myself (1892, p. 266, 



