194 I. IJIMA : HEXACTINELLIDA. I. 



considerably advanced in growth, tlie sclei'oblast-naass 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 with the mass. The numerous, closely packed nuclei do 

 not diffe]-, either in size or appearance after staining, from those 

 of either the trabecular 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 ('g8) 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 plasmodiumAWQ 

 investment to the develoj^ing 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 iu 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 



