+ ia 
STUDIES IN SPICULE FORMATION, 233 
took to work out the histology of the Sycons, more particu- 
larly in reference to the spicules, in order to ascertain whether 
the very anomalous condition of things described by Maas 
had any actual existence or not. I say anomalous condition 
of things, since it was improbable & priori that such a 
fundamental character as spicule formation should materially 
differ in the two subdivisions of the Calcarea, and, as I shall 
show, cautious inquiry entirely disproved the supposition. 
Before proceeding further, I should like to here acknow- 
ledge my great indebtedness to Prof. Minchin, who has so 
kindly afforded me his valuable assistance in the practical 
part of the work and supplied me with information and criti- 
cism in connection with the theory. With reference to this 
latter, however, I had better add that I alone am responsible 
for the speculations advanced in Part II of the present paper. 
Maas’ paper is based on the two species Sycon setosa 
and S.raphanus; the present account applies to Sycon 
coronata and S. ciliata,! both common species on the 
English south coast. The Sycons examined by me were ob- 
_tained from Plymouth, and were prepared as follows :—After 
detachment the specimens were quickly (to ensure full disten- 
sion of the oscular rim) transferred to 1 per cent. Osmicacid, 
in which they remained for some few minutes, and then 
washed with several changes of distilled water; afterwards 
they were immersed in Ranvier’s (Weigert’s is as good) picro- 
carmine for three hours, again washed with changes of dis- 
tilled water, and graded either into 60 per cent. glycerine for 
surface-view examination, or into absolute alcohol for section- 
cutting and surface-view examination. 
These two species of Sycon are cylindrical in form, tapering 
at the two extremities—the basal or affixed, and the apical or 
free. From the base to near the apical extremity the body 
wall of the sponge possesses uniformly-distributed short 
diverticula or chambers projecting from its sides, which 
diminish in size from below upwards, and are, as is well 
1 The process of spicule formation in Grantia compressa also is 
identical with that described for S, coronata, 
