THE president's ADDRESS. 237 



ture must at any rate continue its activities independently of 

 any possible mother-cell, whatever may have been its origin. 



The material at my disposal for the purposes of this inquiry 

 is naturally not well adapted to cytological investigation. 

 Nevertheless it has been possible to make some observations 

 in this direction. In LatruncuUa bocagei I have repeatedly 

 found certain small cells associated with the protorhabds, or 

 with the immediately subsequent stages of development, in a 

 very definite manner. In the youngest stage observed (fig. 1) 

 there is already a distinct indication of such cells forming a ring 

 around the protorhabd not far from the middle of its length. 

 In the specimens represented in figs. 2 and 3 two such rings of 

 cells are clearly visible, one a little above the middle of the 

 spicule and the other about half-way between this and the apical 

 extremity. It seems safe to conclude, from what happens after- 

 wards, that there are normally three cells in each of these rings. 

 I propose to term them the formative cells, for it is evident that 

 they have much to do with determining the manner in which 

 the silica is deposited. What their origin may be I am quite 

 unable to decide, but there seem to be two possibilities. Either 

 they are products of the division of an original mother-cell be- 

 longing to the protorhabd, or they are of extraneous origin and 

 have become associated with the developing spicule secondarily. 

 It seems probable that they continue to divide into daughter- cells 

 as development goes on, and fig. 7 shows faint indications of 

 what may be numerous minute formative cells arranged as a sort 

 of veil around the mature, or nearly mature, spicule. 



A single much larger cell of a very different type is also com- 

 monly found associated with the developing spicule, both in 

 LatruncuUa bocagei, where it may be present together with the 

 formative cells, and in L. apicalis, where the formative cells have 

 not been observed, though there can be little doubt that they 

 are also really present. This cell is clearly shown in figs. 4, 7, 

 14, 15 and 18 (a.s.). It generally has the form of an oval, coarsely 

 granular body with a definite outline. One of the granules may 

 be a good deal larger than the others, and perhaps represents a 

 small nucleus. On the other hand, the entire body itself looks like 

 a very large nucleus, the cytoplasm belonging to which cannot 



JouRN. Q. M. C, Series II.— No. 80. 18 



