STUDIES IN SPICULE FORMATION. 241 
stances that I have observed, the first indication of the 
production of the future monaxon from an isolated scleroblast 
(the “‘ mother-cell”’ of the spicule, Pl. 13, fig. 1) is the enlarge- 
ment of the scleroblast nucleus (fig. 2). This enlargement 
is the precursor to division, and in this manner there is 
produced at the outset the two-celled, i. e. bi-nucleated, con- 
dition of the calcoplasm, which, in Sycons, remains constant 
throughout the entire growth of the spicule (fig. 3). In this 
bi-nucleated scleroblast the nuclei next separate from each 
TEXT-FIG. 3. 
Nc {ily . 
\ . \ \ | \ 
\ \ 
Monaxon spicules drawn with camera lucida from an oscular rim 
preparation, 
other, and aconcomitant of this is the appearance in the cyto- 
plasm of a pale streak (fig. 4; not always easily seen in Sycons, 
though doubtless always present) stretching from nucleus to 
nucleus; it is in the interior of this mould that the spicule 
itself is first deposited as a minute refringent needle. As 
will be seen, the nuclei do not retain this initial position at 
the extremities of the young spicule, but soon come to lie on 
one side, and this fact seems to me to indicate that the 
nucleus is relatively unimportant in the actual secretion of 
lime, or at least of no immediate importance. 
