STUDIES IN SPICULE FORMATION. 253 
growth of the latter for the sole reason that the ship and 
stores do not constitute the building agency—are not engaged 
in the distribution of the added material, but are solely 
concerned with the nutrition of the building elements and the 
supply of material for that which is built. 
A second essential condition to the deposition of lime in 
any quantity in Calcarea (i.e. not taking into account the 
minute granules of lime often found in single scleroblasts) 
seems to be the co-operation of two dermally-derived 
cells, the deposition in every case (as may be inferred from 
the converse of the law just enunciated, viz. that where the 
bulk of the calcoplasm is situated there lime will be deposited) 
assuming an elongated form. ‘l'hus isolated monaxons are 
either formed as above described, on the occurrence of nuclear 
division in a single cell, i.e. on the separation of the substance 
of the cell into two distinct masses at opposite poles, or, as 
there is reason to believe (Appendix B), on the association of 
two cells—in either case two masses of cell-substance with 
their contained nuclei being distinguishable. As also already 
described, it is apparently necessary that each of the consti- 
tuent cells of the trefoil should divide before the three mon- 
axons composing the triradiate can be deposited. And like 
evidence is perhaps afforded by the divided-off small nuclei 
(i.e. cells) of the gastral rays of Clathrina cerebrum, 
each of which doubtless “ co-operates’? with the mother- 
nucleus in order to produce aspikelet. At first sight the 
formation of the gastral ray appears to be an exception to the 
rule, but, seeing that there is no evidence to the contrary, it 
is legitimate to suppose that each gastral actinoblast ‘‘ co- 
operates ” with one or more of the basal cells of the triradiate 
system to produce the ray, and is thus conformable. That 
this is the case is evidenced by other considerations about to 
be discussed. 
Assuming the truth of these two laws—the necessity of the 
proximity of the cell-substance to the site of lime secretion, 
and, in Calcarea, the necessity of the presence of two masses 
ot dermally-derived cell-substance, between which the young 
