80 
ANNIE MATTHEWS. 
secretion upon the food while it is being passed down. The- 
supporting lamella of the stomodaeum always remains a thin 
sheet, while the endodermic lining is similar to that found 
throughout the coelenteric cavity, as the endoderm covering 
the attached base of the polyp is by now reduced to one row 
of columnar cells (PI. 3, fig. 19, End.). In section the top 
of the newly-opened stomodaeum is round, but lower down it 
is keyhole shaped (PI. 4, fig. 34), the narrow ventral end 
of the keyhole being the siphonoglyph. Hence in vertical 
sections which cut the stomodaeum dorso-ventrally, the latter 
seems much wider than when cut in a plane at right angles 
to this. 
12. Spicules. 
Investigation into the origin of the spicule in the young 
solitary polyp confirms Woodland’s work on colonial forms 
( 18 ), adding thereto one or two minor points of interest- 
Each spicule, as he states, is the product of a single cell, and 
during 1 its elaboration the nucleus halves, each daughter 
nucleus apparently controlling one pole of the spicule (PI. 4, 
fig. 31, Nos. 1 and 5). It was found, however, during the 
present investigations that some large spiculoblasts from 
Alcyonium colonies contained three or four nuclei. It was 
also seen that the young scleroblasts are of ectodermic origin 
(PI. 4, fig. 32), and arise as rouud interstitial cells at the- 
base of the ectoderm of the body wall and tentacles (Pl. 5,. 
fig. 35, Sc.). These scleroblasts become stellate, spindle- 
shaped, oval or rounded, as they increase in size (PI. 4,. 
fig. 32), and, as explained previously, are encroached on and 
eventually surrounded by mesoglea, either singly or in small 
groups. In later stages the spicules become entirely isolated 
from one another by mesogloea. As Woodland states, the 
cytoplasm of the scleroblasts eventually becomes reduced to a 
mere thin granular covering-layer over the greatly enlarged 
spicules (PI. 4, fig. 31, Nos. 4 and 5). PI. 4, fig* 30, shows 
that after dissolving away the spicules by an acid stain 
(picro-nigrosin), the mesogloea is left full of corresponding; 
