ON -MElv'LIA XOKMAXL 679 



(c) canalar epithelimn ; (d) myocytes ; (e) scleroblasts ; (f) 

 choanocytes ; (c) auiuobocytes ; (h) tokocytes. 



(a) Colleucytes or Connective-Tissue Cells. 



The connective-tissue cells or collencytes (PI. 87, fig. 2) 

 are finely granular with an uval vesicular nucleus devoid of 

 a distinct nucleolus, and with branching processes which 

 anastomose with those of other collencytes to form a network. 

 The ground substance or maltha at first sight seems almost 

 homogeneous, but in good preparations under a high power 

 it shows a very finely fibrillar structure. When bundles of 

 fibrin^ are cut across they form finely granular areas in 

 section (PI. o4, fig-. 4). 



(e) Gland -cells and cuticle. 



The sponge surface is often coated over with a very thin 

 layer of structureless cuticle, apparently the product of 

 elongated granular cells vertically orientated just below the 

 surface (PI. 87, fig. 4). In these cells there is a minute dark 

 body like a nucleolus, but situated just outside the vesicular 

 nucleus. 



(c) Canalar Epithelium. 



A remarkable feature of great interest, and, I believe, 

 unique, is the absence of a surface layer of epithelium. In all 

 the best preserved material I found the cells at the surface 

 precisely the same as those in the body of the sponge, i.e. 

 they were branching collencytes Vv'ell separated from each 

 other by the maltha in which they were embedded. Knowing 

 how difficult it often is to see the outlines of surface epithelial 

 cells, at first I concluded that the cuticle — usually, but not 

 always present — was an epithelial layer. Further, in one or 

 two very contracted specimens, which had not been properly 

 fixed, the collencytes had become so pressed down in the 



