548 W. WOODLAND. 
at a conclusion, and, worse still, publishing it as an ascer- 
tained fact. 
Gerould, in 1896, supplied a figure showing a young ter- 
minally-bifurcated rod of Caudina arenata with five sclero- 
blasts either near or attached to the spicule, but he evidently 
did not attempt a systematic research in this direction. 
A Few THEORETICAL CONSIDERATIONS. 
Those who have read Prof. Minchin’s admirable account 
(6) of spicule formation in the Clathrinid Ascons, or Study I 
(and II) of the present series, will have been struck by the 
Trxt-Fic. l. 
a. Young monaxon spicule of a calcareous sponge. 8B. Young Aleyonarian 
spicule. c. Young Cucumarian spicule. 
curious fact that, whereas the young spicular needle or 
rod of sponges (and Alcyonaria) is situated in the line joining 
the two primary scleroblasts, that of Cucumaride is dis- 
posed transversely to this line (fig. 4; and text-fig. 1). 
Is this fact to be correlated with any other conspicuous 
difference in the structures associated with the spicule in the 
respective groups? ‘The only difference, and that an import- 
ant one, which suggests itself to me is the evident difference 
of constitution of the scleroblast substance in sponges and 
Cucumariide. As remarked upon above and also in 
Study II, whereas in sponges the young spicular needle 
originates in the deep interior of the substance of the sclero- 
blast, and, in correspondence with this quality of the cell 
substance, the scleroblast of the grown spicule adheres to its 
mass as a sloping mound containing the nucleus, in the 
echinopluteus the young spicule originates in the ectoplasm 
