256 W. WOODLAND. 
If the supposition hitherto made, viz. that the association 
of scleroblasts in twos and threes is largely, if not entirely, 
fortuitous, or, at most, only due to those influences which 
lead to conjugation and syzygy in Protozoa, be legitimate, 
then it follows that higher associations must also occur, and, 
if such be the case, there must be an explanation of the fact 
that four- and five-rayed spicules are rarely, if ever, met 
with.! On mere grounds of probability these higher asso- 
ciations must be few in number, and in observations of the 
sponge-wall they would probably be passed over as stages in 
the tormation of sextets, but I have no doubt that systematic 
search on a large scale would reveal their existence.” Why 
these higher associations do not result in multi-rayed spicules 
can be explained as follows :—Suppose four cells to associate, 
then, as in the case of the trefoil, and for the same reasons, 
neither a central concretion nor a square of monaxons would 
be deposited. But, assuming that the four cells are 
triradiate form so often observed in these spicules, as e.g. in Clathrinide. 
And in this minor objection I largely concur, as is proved by the fact that 1 
have on p. 271 named additional factors capable in my opinion of producing 
the remarkable regularity characterising the spicules of Clathrinide, and have 
further on p. 270 supplied other reasons as to why the spicules of Leucoso- 
leniide, Sycons, and sponge larve should be more irregular in form, At the 
same time I believe that, in the very young spicule, the regular triradiate 
form (conspicuous at the basal insertion of the rays in the most irregular of 
adult spicules) is solely due to the initial triradiate construction of the trefoil. 
Prof. Minchin’s objection on the score of the one-sidedness of the cell to the 
ray has little weight, as I have shown in the footnote on p. 252. The cell 
situated on a monaxon secretes a straight ray despite its one-sideduess, and 
if this asymmetry of position is of such little account in the production ol a 
monaxon spicule, why should it be of so much importance in the development 
of a triradiate ? 
' Prof. Minchin has shown me an anomalous equiangular spicule in an 
Ascon sponge consisting of five rays in one plane. As explained below, it is 
probable that this rare form of spicule resulted from a chance association ot 
five cells, which happened to be so symmetrically disposed with respect to 
each other as to prevent a rcsolution of the cell congeries into triradiate and 
monaxon groups. 
2 Groups of cells occasionally occur which are not as a whole recognisable 
as developing or developed sextets. 
