292 W. WOODLAND. 
explanation of this difference of form in the two cases is the 
difference of situation of the young spicules drawn by Bourne 
and of those drawn by myself—Bourne’s spicules being loca- 
lised in a mobile portion of the colony (the bases of the 
polyps, where the mother-cell is obviously subject to disturb- 
ing influences which might very possibly lead to irregularity 
of form of the contained spicule) and mine in a quiescent. 
But, apart from this, some of Bourne’s figures (e.g. his fig. 4) 
certainly suggest the idea of his spicules having been subjected 
to rough treatment of an artificial kind, such as the stretching 
open of the polyp, and the brushing of its internal wall might 
by chance involve, but whether the fractured appearance of 
the spicules suggested by Bourne’s figures is due to this, or 
to the above-mentioned cause or to the mode of drawing, I 
am unable to say. Certainly the young spicules observed by 
me did not exhibit this broken irregular appearance. 
As just stated, up to the division of the scleroblast nucleus, 
the form of the young spicule remains smooth and approxi- 
mately spherical, but when this change in the nucleus occurs, 
the spicule becomes elongated and somewhat dumb-bell in 
shape (not dumb-bell in shape in the sense in which Hickson 
refers to adult spicules), i.e. thickened and rounded at the 
two extremities, and the two nuclei, which form centres for 
the aggregation of the cytoplasm, in general travel to its 
opposite ends. This simple dumb-bell then enlargens and its 
two extremities become amphiccelous by the development of a 
broad rim round the terminal surface of each “head” of the 
dumb-bell (figs. 3 and 4). Following on this again, the rim 
on the terminal surface becomes developed into two, three, 
four, or more processes, some, or occasionally all, of which 
afterwards become the main branches of the spicule; other 
smaller processes may also appear, and the spicule now 
assumes the form depicted in figs. 5and 7. This stage thus 
reached forms in the vast majority of cases the basis of all 
future development, since it is a ground plan common to, and 
recognisable in, all spicules whatever shape they may ulti- 
mately assume (with the possible exception of the spindles 
