382 E. W. MACBRIDE. 
observed, is the only one of the great ‘‘schizoccelic”’ spaces 
which Hamann (8) has described in the body-wall which has 
any real existence, the others being merely artefacts produced 
by the process of decalcification. I have found one specimen 
showing the first trace of a dermal branchia (figs. 96 and 97). 
We see a slight thickening of the peritoneum, and above it the 
peribranchial space. Fig. 96 shows that the latter is a diverti- 
culum of the ceelom. As I have only one section illustrating 
this I do not speak with absolute certainty on the point; but, 
with this possible though very improbable exception, there is 
no schizocele whatsoever in Asterina gibbosa: all 
spaces lined by epithelium are of celomic origin. 
Histological Differentiation. 
The cells of the gut-wall have undergone some change since 
the close of the metamorphosis. Specimens of the epithelium 
from different regions are given in Pl. 26, figs. 129—132. These 
are all taken from a young adult in which R equals ‘85 milli- 
metre. The cells of the lateral walls of the stomach (i.e. the 
adult oesophagus) have become exceedingly long and narrow ; 
their outer ends are refracting and take a light yellow tone 
with osmic acid (fig. 129). The cells of the aboral wall, on 
the contrary, have developed numerous gland cells filled with 
globules; interspersed amongst them are some very narrow 
filamentous cells. Fig. 180 shows the spot marked x where the 
stomach opens into the pyloric sac and the abrupt change 
in the character of the epithelium. The pyloric sac is lined 
by uniform columnar cells; the nucleus is generally near the 
base of the cell, and is never placed further up than the 
middle, and the protoplasm is uniformly granular (fig. 131). 
The cells lining the rectal ceecum (fig. 132) are similar in form 
but smaller, and the protoplasm is clearer, with the outer part 
more refringent. It is at least a plausible suggestion that the 
gland cells of the stomach secrete the poison which paralyses 
the prey, and that the cells of the pyloric sac give rise to a 
digestive ferment. 
The differentiation of tissues which has gone on in the 
