409 
Mr Menon, Notes on Semper’s Larvae. 
The macromesenteries have well-developed mesenterial fila- 
ments. Gland cells and occasionally the larger kind of nematocysts 
are seen in them. 
The deeper layer of the ectoderm is in places closely packed 
with the larger kind of nematocysts. It is very rarely that a 
whole nematocyst, with capsule and thread, is seen. What one 
generally finds is a number of threads loosely and irregularly 
coiled, lying in large oval spaces in the deeper parts of the ecto- 
derm ; their capsule is visible. These threads are very conspicuous 
structures in transverse sections. The smaller nematocysts are 
very numerous in the superficial layer of the ectoderm. The 
colour of the larva is due to the numerous pigment cells in the 
ectoderm. The mesogloea is a homogeneous membrane, thicker 
in some places than in others. It contains cell-elements of two 
kinds, small, clear, ovoid cells and large, round, granular cells. Of 
these the former seem to be derived from the similar cells which 
lie here and there in the ectoderm, immediately next to the 
mesogloea, just in the same way as the large, granular cells are 
derived, as is indeed stated by Yan Beneden, from the deeply 
staining cells which lie here and there on the inner face of the 
mesogloea. The cells of the mesogloea lie in spaces which are 
often seen without the cells. They do not form strands, as in 
Zoanthina. 
The endoderm is a layer of great thickness. It is thin in the 
region of the stomodaeum, but increases in thickness aborally. In 
sections passing a little below the lower end of the stomodaeum 
the endoderm forms large masses almost filling up the mesenteric 
chambers, with their rounded inner ends projecting into the 
coelenteron. The endoderm covering the faces of the mesenteries 
forms a comparatively thin layer. About a quarter of the animal’s 
length from the aboral end the endoderm almost fills up the 
coelenteric cavity, a small irregular space in it representing the 
much reduced coelenteron. Still lower down the cavity disap- 
pears altogether. The endoderm is highly vacuolated and con- 
tains numerous scattered nuclei. This condition of the endoderm 
is interesting inasmuch as it shows that the explanation sug- 
gested by G. C. Bourne of a similar condition of the endoderm in 
Euphyllia, viz., that the great development of the vacuolated 
endoderm filling up the coelenteron is connected with the pre- 
sence of a large number of Zooxanthellae, is not applicable to all 
such instances. The endoderm covering the dorsal and ventral 
faces of the macromesenteries as well as the whole of the endo- 
derm covering the micromesenteries, consists of large granular 
cells or masses of cells with one or more nuclei. It stains very 
deeply. Similar deeply-staining cells often form a core to the 
large vacuolated masses projecting into the coelenteron. The 
