MATERIALS FOR A MONOGRAPH OF THE ASCONS. 38138 
found a similar course of events in the formation of the mon- 
axons of Sycon. Maas, however, has given a description of 
the formation of the monaxons of Sycandra setosa, which 
is at variance with our results (1900 [2j). He finds the 
small monaxons developing each in a single cell, but the 
larger monaxons, on the other hand, being built up by 
numerous cells. It may be pointed out, to begin with, that 
Maas has described these appearances from sections, which 
is an unsafe proceeding. I should interpret his fig. 23 on 
Pl. 11, as representing one of the two cells present, probably 
the thickener, on each of the three spicules depicted, the 
other cell having been cut away or overlooked. Again, his 
fig. 25, intended to represent a large monaxon with many 
cells on it, is not convincing to me, as it is not possible with the 
magnification given (300) to determine the relation of the 
cells to the spicule. The drawing shows six rounded cells on 
or over the spicule, none of which look at all like scleroblasts. 
I may remark that the monaxon in question is very much 
smaller than the large monaxons of L. complicata (com- 
pare my figures of the spicules at the same magnification 
[1905 (2)]), and that in this case, as already described, I 
have found never more than two cells present on the spicule. 
I regret, therefore, that I am unable to accept my friend’s 
figures as evidence for the correctness of his statements, 
which appear to me to require revision. 
A monaxon spicule which develops, like a single ray of a 
triradiate, from two formative cells derived by division of a 
single mother-cell, is a spicule which I should regard as a 
primary monaxon. So far as the observations of Woodland 
and myself extend, the monaxon spicules of Leucosolenia 
and Sycon are all primary. There is no reason why a mon- 
axon spicule should not arise secondarily, by modification of 
a triradiate, that is to say, by loss of one ray and placing the 
two remaining in a line with the other. I have elsewhere 
(1905 [8]) given reasons for regarding the huge monaxons 
of Clathrina contorta as secondary in nature, and I feel 
convinced that the same applies to the elbowed monaxons in 
