142 W. WOODLAND. 
cipals contained within. Later, after the terminals have 
considerably advanced in growth, the scleroblast-mass appears 
at the centre of the developing hexasters as a more spherical 
body, not unlike a berry, on account of the aggregated 
nuclei.” “Not a trace of cell-outlines is discernible around 
them [the aggregated nuclei], which fact makes me believe 
that the scleroblast-mass represents a syncytium.” And, 
referring to the prevalent but mistaken notion that the 
scleroblast nuclei change their position in order to superintend 
the process of deposition in different regions of the spicule, 
Ijima remarks :—“ Certain it seems that, during the growth 
of the terminals, no nucleus moves away from its group 
around the spicular centre. At least I could gather no 
evidence pointing to such a movement. It is true that, after 
a certain period in the growth of terminals, a variable number 
of nuclei is met with right away, or in close proximity to, 
these. However, they are altogether so inconstant in number 
and indefinite in position that it is exceedingly questionable 
if they have anything to do with the building up of the 
terminals.” My figures confirm all the preceding remarks. 
Fig. la depicts a stage in which the terminals have not nearly 
reached the surface of the spherical syncytium, and which is, 
therefore, younger than any figured by Ijima. Ijima goes on 
to remark concerning the “great probability . . . that each 
growing terminal is completely invested by an extremely thin 
protoplasmic layer, specialised physiologically at least as the 
secretive matrix, and standing in direct continuity with the 
scleroblast-mass. Such a layer, however, could never be 
clearly demonstrated.”! I may say that I have many times 
observed in my preparations the film of scleroplasm which 
invests the terminals of both young and old spicules (and 
which I have endeavoured to represent in figs. 3 and 6), 
although this is not by any means always visible; in fact, 
usually is not. ' 
As shown by my figures the scleroblast-mass varies con- 
1 ]jima, however, in a later contribution (16) describes and figures this 
layer in the oxyhexasters of Rhabdocalyptus capillatus. 
