320 KH. A. MINCHIN. 
I have already stated, the gastral ray owes its origin to a 
granular cell which joins itself to the six formative cells of 
the triradiate system to form a septett. In Clathrina I 
was able to show that this cell, the gastral actinoblast, arose _ 
from a porocyte, or from one of the epithelial cells, lining 
the interior of the gastral rim, from which porocytes arise. 
In Leucosolenia the characters of the gastral actinoblasts 
leave no doubt in my mind that they have an origin similar 
to those of Clathrina, but I am not able to bring forward 
such definite proof of this statement. This is one of the 
points in which I had hoped to have completed my observa- 
tions. I may draw attention, however, to the section figured 
in fig. 54, in which the cell (p.c.) could be interpreted as a 
gastral actinoblast in the act of migration from the neigh- 
bouring pore. 
In L. complicata the nucleus of the gastral actinoblast 
divides sooner or later into two. Sometimes the division 
takes place very early (fig. 24). 
There is little to note with regard to the growth of the 
gastral ray itself; it is sufficient to refer to the illustrations 
given (figs. 24—28, 60—70). I may draw attention, however, 
to the fact that the gastral ray of L. complicata arises far 
behind the junction of the three basal rays (figs. 24—26, 28, 
52). ‘This point is noticeable in the full-grown spicule, but 
much more so in the early stages of growth. Hence even 
quadriradiate spicules, at their first appearance, are utterly 
unlike the primitive tetraxon form, from which some authors 
derive all the spicules of calcareous sponges. 
With regard to the cells found upon the gastral ray some 
remarkable peculiarities can be observed. One is the ten- 
dency of the cells to become increasingly granular, some of 
the granules being of large size and taking a pink stain with 
picrocarmine. Another point is the presence in many cases 
of additional cells of a peculiar kind on the full-grown gastral 
ray (figs. 64—67, ex.c., 69) ; a point which I shall have to deal 
with under a separate heading. ie 
As regards the gastral rays formed in the region of the 
