QA8 W. WOODLAND. 
the presence of the diverticula, but certain facts tend to the 
conclusion that the origin of the gastral actinoblast is the 
same as that found in the Ascons. In this group,as Minchin 
has shown in detail, the mother-cell is produced by the 
division of a pore-cell in the vicinity of the future quadri- 
radiate (when this is situated in the body of the sponge; 
when the triradiate is situated in the oscular rim, the mother- 
cell is supplied by one of the unspecialised cells of the 
epithelium in that region), the resulting scleroblast settling 
over the point at which the gastral ray is to be developed, 
and, without further division, secreting a calcareous mass 
which adheres to, or near to, the centre of the triradiate 
basis, and gradually assumes the form of the adult ray. 
Evidence for the assumption that a similar state of things 
occurs in the Sycons is afforded by the general similarity of 
spicule formation found in the two subdivisions, and by the 
fact that pore-cells are generally situated in the neighbour- 
hood of gastral rays. 
The youngest stages of development of the gastral rays 
which I have observed in sections of Sycon coronata are 
represented in figs. 35 and 36, in which the mother-cell must 
be distinguished from the basal cell or cells belonging to the 
triradiate basis. It must be pointed out that the figures 
given of the succeeding stages of gastral ray development 
represent the formative cell or cells as being more or less 
limited in respect to the area of the ray over which the cell- 
substance extends, and such they appear to be in the ordinary 
picro-carmine preparations,! but if the sections be immersed 
in Kernschwarz for ten minutes or so, the cell plasma (in 
which granules are scarce) becomes stained, and is seen to 
more or less entirely envelop the gastral ray whatever the 
stage of development may be (fig. 38). In studying the 
1 The numerous figures given of the picro-carmine stained actinoblasts of 
the monaxon and triradiate spicules are correct, the cell-substance being, as 
shown, strictly limited in these cases (see p. 250); only the actinoblasts of 
the gastral rays of quadriradiates are entirely enveloped by the cell- 
substance (p. 250). 
