STUDIES IN SPICULE FORMATION. 149 
the cells in connection with the adult tylostyle are quite 
incorrect. These never have either an epithelial! disposition 
or the “syncytial” disposition shown; on the contrary, each 
of the several “cells” (i.e. nucleated portions of the syn- 
cytium) in connection with the elongated spicule forms a 
sloping mound-like mass containing the nucleus, and lies in 
close apposition with the spicule, as depicted in my figure of 
the Hsperella monaxon (fig. 19). 
Maas’ second statement I believe to be not more valid 
than the first. The chiaster, according to my observations, 
originates, like the spheraster, as a granule contained within 
the cell, and this granule, also like that of the spheraster, 
develops rays on its surface (fewer in number? and relatively 
longer and more uniform in thickness as compared with those 
of the spheraster) which become those of the adult chiaster 
(figs. 20 c, g). The mother-cell, as Maas states, remains 
undivided. | 
Maas’ third statement is also contradicted by my observa- 
tions. I can find no evidence whatever that the spheraster 
ever passes through a calthrops stage; on the contrary, it 
develops in almost exactly the same way as the chiaster. 
The initial granule develops numerous radiating rays whilst 
quite small (Maas’ fig. 7 is quite correct e. g.), and from this 
ground form (figs. 20 b, d) the adult spicule is formed 
(figs. 20 h, 7, k) by the further accretion of silica, and also, 
I believe, by the occasional development of fresh rays during 
the early stages. As implied above, these rays of the sphe- 
raster are more numerous and more conical in form than 
those of the chiaster, and these differences alone distinguish 
the younger developmental stages; at first indeed it is very 
1 Maas makes the same mistake in connection with the monaxon spicule of 
Sycandra, figuring the half dozen scleroblasts as spherical cells just 
touching the surface of the spicule. Scleroblasts never have this arrangement 
in connection with spicules or, so far as I know, elsewhere. 
* Even if, as occasionally may be the case, these spines of the developing 
chiaster are four in number, this fact affords no justification for Maas’ state- 
ments in connection with the spheraster, 
