70 
ANNIE MATTHEWS. 
while nematocysts are very abundant over the whole surface. 
The long planula-shaped polyp now shrinks in length (Text- 
figs. 10, 11, and 37), the ectoderm and supporting lamella 
each becoming crumpled up on itself so that it is of wavy 
outline in section. The endoderm cells are indeed heaped up 
into a series of blunt processes separated by deep hollows, and 
projecting into the ccelenteron (Text-fig. 37, End. C.). Soon 
the pointed aboral end flattens down, the larva in vertical 
section now appearing like PI. 4, fig. 23. The endoderm 
is a single row, except at the base, where it forms a deep 
multilayered mass of cells each containing one huge vacuole 
(in stained preparations). Thus a mound-like stage is reached 
at the end of the first day of sedentary life. A little later 
the mesenteries arise, and simultaneously a great and rapid 
increase in the number of rounded cells at the base of the 
columnar ectoderm occurs all over the surface. Next these 
become surrounded by mesogloea, and from now onwards an 
intermediate layer separates the endoderm and ectoderm of 
the polyp. The rounded cells are young scleroblasts and 
nematocysts. 
The next section of the paper deals with the secretion of 
mesogloea, as the further development of the polyp may then 
be more easily understood. 
9. Mesoglcea. 
In this paper the word mesogloea 1 will be applied to the 
structureless, deep-staining, jelly-like substance which lies 
between the ectoderm and endoderm of the polyp, and, aided 
by the spicules, gives rigidity to the body wall. The “ endo- 
mesogloeal ” cells are the cells which become embedded in it. 
The thin supporting lamella which first appears between the 
endoderm and the ectoderm of the late pre-planula, and can 
be traced in the planula (PI. 4, fig. 27, S. M.) and earliest 
settled stages, stains quite similarly to the mesogloea of later 
1 This word was introduced with the significance given above by 
Prof. Gilbert Bourne, F.B.S., in 1887 (see ‘ Quart. Journ. Micr. Sci./ 
vol. 27, p. 303). 
