194 I. IJIMA : HEXACTINELLTDA. I. 



considerably advanced in growth, tlie scleroblast-raass appears at 

 the center of tlie developing hexasters as a more spherical body, 

 not unlike a berry, on account of the aggregated nuclei (figs. 31, 

 33, 34). 



The protoplasm of the scleroblast-mass is finely granular 

 and is stained in about the same degree as the trabecular plasma. 

 The contour at the external surface is indistinct ; sometimes it is 

 tolerably well defined and is found to be either irregular or 

 moderately even. There is never a delimiting membrane in 

 contact Avith the mass. The numerous, closely packed nuclei do 

 not differ, either in size or appearance after staining, from those 

 of either the trabeculœ or the archseocytes. Not a trace of cell- 

 outlines is discernible around them, which fact makes me believe 

 that the scleroblast-mass represents a syncytium. 



Here I am reminded of Minchin's ('98) statements with 

 regard to the development of calcareous spicules, of which he 

 says that the formative cells in a sextet appear to fuse together 

 at the center, where the first secretion of the rays of a triradiate 

 spicule soon afterwards takes place ; and also that the nucleus of 

 the cell, which gives rise to a fourth ray in forming a quadri- 

 radiate spicule, may divide, thus forming a jjlasmodiwn-MX^Q 

 investment to the developing ray. Whether the agreement sug- 

 gested between the state of the formative cells in the Calcarea 

 and that of the Hexactinellida is of any real import, I am not 

 prepared to say. 



The number of nuclei in the scleroblast-mass may possibly 

 stand in relation to that of terminal rays in, or to the size attained 

 by, the hexaster to which it gives rise. At all events as a 

 matter of fact, I have found the nuclei most numerous in the 



