156 I. IJIMA : HEXACTINELLIDA. I. 



Schulze had before in E. aspergillum associated with the con- 

 nective substance, instead of classing them as flat epithelial cells. 

 I am decidedly in favor of this older view of Schulze's. The 

 cells in question, as known to me from Euplectella and a number 

 of Hyalonematids, Rossellids, <&c., — which cells I have no doubt 

 belong to one and the same class of cells both morphologically 

 and physiologically, — always have plump bodies and show clearly 

 defined cell-boundaries, lohich as a rule are well separated from 

 one another. In most species, e.g., E. marshalU, they are 

 ordinarily quite sparingly and isolatedly present, while in certain 

 places and under special circumstances they may occur in large, 

 compact masses (PI. IV, fig. 24). (See anon under Thesocytes). 

 These facts in my view militate against the propriety of attri- 

 buting to the cells an epithelial nature, in spite of their most 

 superfi.cial situation. Even granting their epithelium-like arrange- 

 ment, their homology with the true pinacocytes may be questioned, 

 because the latter cells, so far as my knowledge of them goes, 

 are never known to have similar contents, Avhile certain other 

 cells which do possess such contents — i. e,, the thesocytes, which 

 are not improbably identical cells in all sponges of different 

 classes — are found scattered invariably in the mesenchyme of such 

 sponges as show besides a true pinacocytal epithelium. 



It is important to note that Schulze did not find in 

 Schaudinnia arctica the alleged epithelial cells on all parts of the 

 trabecular systems. They were evidently not present on the 

 finer intercatneral, subdernial and subgastral trabeculœ. " Es 

 könnte daher sein, dass diese Verbindungsbalken einer besonderen 

 epithelialen Bekleidung entbehren und ganz aus der...Biudesub- 

 stanz bestehen " ('99«, p. 208) is his conclusion. While main- 

 taining the presence of an epithelium on the thicker trabeculœ, 



