48 ART. 7 1. IJIMA : HEXACTINELLTDA, IV. 



the inner mass exposed at these parts. The cell-bodies take up 

 stains well, on which acconnt evidently the nnclei can not be 

 perceived with any degree of distinctness. Notwithstanding thi>'=' 

 fact it seems assumable that the single bodies here taken for the 

 cells are not merely nnclei by themselves. The cells, as seen in 

 both cross (fig. 21) and tangential (fig. 19) sections, are separat- 

 ed from one another by narrow clear spaces. 



Internally against the inner mass the covering layer is 

 sharply delimited. On the external snrface, so far as the pre- 

 sence of the layer can l)e demonstrated, there is a coating of 

 qnite clear appearance, showing a sparse granulation which here 

 and there assmnes the form of a vertical striation. I think 

 there is no doubt whatever that this coating represents the fla- 

 gella, which have deteriorated as the result of the application of 

 reagents. The same was observed likewise in the larva of Len- 

 copsacus orthodocus (Contrib. III., p. 43) ; therefore the Hexacti- 

 nellida seem to offer no exception to the rule that the sponge- 

 larva is provided with an external layer of flagellated cells. 



The inner mass, as seen in toto preparations under a mode- 

 rately high power of the microscope (PI. III., fig. 20), ajipears, 

 leaving aside the spicules, simply as a dense assemblage of well- 

 stained corpuscles, much like a large congeries of the archseo- 

 cytes before spoken of. Closer observations on serial sections 

 (subjected to after-staining with hematoxylin or hsematein-alum 

 or with either of these in combination with eosin, &c.) reveal 

 that to a certain degree histological differentiation already exists 

 among the elements of the mass (PI. Ill,, fig. 21). 



Peripherally and right under the external epithelium, the 

 corpuscular elements, in respect to which it is difficult to deter- 



