MATERIALS FOR A MONOGRAPH OF THE ASCONS. 3817 
furnished by the development of the monaxons, it would be 
quite feasible to regard each sextett as having arisen by the 
immigration of six cells independently from the dermal layer, 
The cells of the sextetts are very irregularly disposed, and it 
is difficult, often impossible, to pair them off, so to speak. 
Frequently a seventh cell, slightly more granular than the 
remaining six, is found, forming a septett; in these cases 
the spicule is destined to be a quadriradiate, and the seventh 
cell is a gastral actinoblast, the mother-cell of the gastral 
ray. I have never observed, however, the gastral actinoblast 
to be present until the triradiate system has begun to be 
formed and has reached a certain size. 
Although I have examined carefully some hundreds of 
young stages in the formation of calcareous triradiate systems, 
both im my preparations and in those of Woodland, I have 
never seen anything but the two conditions I have just 
described, that is to say, either six or seven cells. Urban 
(1905, Pl. 6, fig. 34) has figured, however, a triradiate system 
with more than six cells upon it. Iam inclined to think that 
this author -has not clearly distinguished between formative 
cells adherent to the spicule, and cells of the overlying 
dermal epithelium. It is very easy to confuse the two. 
More difficult for me to understand are the statements of 
Maas (1900 [2]), who claims to have found the quadriradiates 
of Sycandra setosa arising each in a single cell (I. c., 
Pl. 11, fig. 24, i—ii). This statement is so directly at 
variance with all my experience on the subject that I am 
unable to support my friend’s statements. I think the dis- 
crepancy in our observations may be explained in the follow- 
ing way. In the septett of cells covering a young quadri- 
radiate the gastral actinoblast is far more granular than the 
formative cells of the basal system, and this difference is 
accentuated if alcohol is used as the preservative (which was 
Maas’s method) instead of osmic acid (which I always 
employ). Looking down upon the septett from the gastral 
aspect, the gastral actinoblast would be obvious, but the 
cells of the underlying sextett might easily be overlooked if 
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