72 
ANNIE MATTHEWS. 
before it becomes surrounded by mesogloea. Evidence seems 
to indicate that the mesogloea flows out from the endoderm 
(Pl. 5, figs. 36 and 39). It is certainly not secreted by any 
of the ectoderm cells, and the direction of flow is always out- 
ward from the endoderm to the ectoderm, and then, as 
previously stated, in among and around the basal cells of this 
layer. During the later growth of the mesenteries they con- 
sist almost wholly of a thin sheet of structureless mesoglea, 
covered on both sides by endoderm (PI. 5, fig. 38, Mg l and 
End.), so that this layer is probably capable of providing for 
all further secretion of mesogloea required by the growth of 
the mesenteries (see paragraph on mesenteries). 
Nothing has been found to correspond with the irregular 
nells described by Bourne (1), full of minute highly refringent 
granules, which concealed the nucleus. He suggested that 
these might be the mesogloea-secreting cells, while Woodland 
( 18 ) described some small rounded cells which he also noticed 
as full of refringent granules, without deciding whether these 
corresponded to Bourne’s. As both these papers were founded 
on work done on Alcyonium colonies, cells may be present in 
the mesogloea which are not found in the solitary polyp. Still 
it seems very possible that Woodland’s cells were merely 
young scleroblasts, judging from his figures. The “oval 
bodies ” described by Hickson ( 3 ) and Woodland as occurring 
in the mesogloea are nematocysts which may be in process of 
migration. The coiled thread in the cell was clearly stained 
with picro-nigrosin after preservation with osmic acid (PI. 3, 
fig. 22, N. T .) 
10. Mesenteries. 
The eight characteristic mesenteries of Alcyonium are thin 
vertical sheets stretching radially into the coelenteron from 
the body wall and dividing it into eight incomplete inter- 
mesenteric compartments, without meeting one another in the 
centre. They consist of thin sheets of mesoglceal substance 
arising from the supporting lamella of the body wall (PI. 3, 
fig. 19, Mes.), and covered on both sides by endoderm cells 
