MATERIALS FOR A MONOGRAPH OF THE ASCONS. 303 
Woodland has also done) that my figures and investigations 
on calcareous spicules antedate his, though published later.! 
In my former memoir (1898) I went fully into the literature 
of spicule-formation in sponges and discussed the various 
statements of fact or theory made by those who have written 
upon-this subject.2, I may refrain from discussing further 
the historical side of the subject, since most of the papers 
dealing with the spicules of sponges that have been published 
during the past few years will be found quoted by me, with 
brief abstracts, in the £ Zoological Record’ (1900—1903). I 
shall therefore only refer to the statements of other authors 
as occasion arises. In one point the published statements 
upon spicule-formation led me astray in my former memoir. 
Having then had no opportunity of investigating primary 
monaxons in the Clathrinide, | took for granted the cor- 
rectness of previous statements upon the formation of monaxon 
spicules in sponges with regard to one point, namely, that 
each such spicule developed and grew in a single cell. 
This alleged mode of development was an obstacle to my 
comparison of the triradiate spicule to a system of three mon- 
axons joined together, since each ray of a triradiate is formed 
from the first by two cells. When I came to investigate the 
monaxons of Leucosolenia, however, I found that each 
spicule of this class, whatever its size or form, arose invari- 
ably in two cells, exactly as does a single ray of a triradiate 
system. ‘This fact had previously been observed by Bidder 
(1898, p. 62, foot-note) in the case of the hair-like spicules of 
Grantia compressa, and was regarded by him as specially 
characteristic of this type of monaxon ; but from the observa- 
tions of Woodland and myself, it would appear to be uni- 
1 [ take this opportunity of remarking that I regard Woodland’s “ Studies 
in Spicule Formation” as constituting a most valuable contribution to our 
knowledge, so far as matters of fact and observation are concerned ; but that 
in matters of theory I am often unable to see eye-to-eye with him. I may be 
obliged in the course of this memoir to controvert his speculative opinions. 
? Maas (1900 [3], p. 555) is very charitable to me in attributing to design, 
and not to inadvertence, the fact that in my memoir (1898) I overlooked the 
statements of Desz6 on spicule-formation in Tethya. 
