166 I. IJI3IA : HEXACTINELLIDA. I. 



Hexactinellid species as ^Yill be demonsti'ated in the course of tliis 

 series of Contributions, are spherical or approximately so ; some- 

 times ihej are ovoid and, when several lie close together, they 

 may by mutual pressure approacli a polygon in shape. In dia- 

 meter, they measure only 2-372 ,«, rarely as macli as o /'. The 

 variation in size is mainly due to the greater or less quantity of 

 the cytoplasm which is on the whole sparingly present, being 

 represented by a thin layer around the nucleus. The outer 

 contour of the cell is even and distinct, without any indication 

 of the presence of an investing membrane. 



The cytoplasm appears nearl}^ homogeneous. Osmic acid 

 slightly browns it. In specimens hardened with corrosive-sub- 

 limate or with absolute alcohol, it takes up coloring matter very 

 well, so that the outline of the nucleus within is somewhat ob- 

 scured. If this fact is considered together with the smallness of 

 the cells, which are often of nearly the same size as the trabe- 

 cular nuclei, there ought not to be much wonder if the cells 

 should be thrown together with the latter uuder the nuclei, in- 

 stead of being recognized as complete cells. In fact, in my 

 earlier notes and sketches concerning not only li!. marslialli, but 

 also a number of other species in which I later recognized their 

 true nature, I find them put down as nuclei ; and I venture to 

 say that F. E. Schulze possibly fared similarly in his study of 

 Schaudinnia arciica (see ante, p. 159). Examined under an 

 immersion system in successful preparations, the cell-body stands 

 out as distinctly as I have represented it in PI. V, figs. 37 and 43, 

 inclosing an indubitable nucleus which in its turn contains darkly 

 stained chromatic bodies. Whereas, if seen under only a moderate 

 power, the entire cell-body might easily pass for a nucleus and 

 the real nucleus for a chromatic inclosure. 



