411 
Mr Menon, Notes on Semper s Larvae. 
The syncytium presents a new appearance. The central portion 
has separated off from the peripheral and lies in a central cavity into 
which the stomodaeum opens. In sections passing through the oral 
half of the larva this central portion is not seen ; in this region, 
therefore, the mass has already broken down, giving place to a 
cavity which occupies the whole of the interior of the larva. The 
vacuolated peripheral portion of the syncytium containing a little 
yolk becomes the endoderm. The central portion, which is also 
vacuolated and contains yolk, has quite disappeared in the follow- 
ing stage, having, no doubt, been resorbed. In this stage, a section 
of which is shown in fig. 7, the central cavity is lined by a 
vacuolated endoderm layer containing scattered nuclei and small 
rounded granular masses of yolk. The endoderm thus apparently 
does not at any stage consist of regularly arranged cells like the 
ectoderm, but is from the beginning a vacuolated syncytium which 
in later stages becomes enormously developed and fills up the 
greater part of the coelenteron. 
The coelenteron thus arises by the splitting of the inner mass 
and becomes definitely established by the breaking down and 
resorption of part of that mass. 
In the stage represented in fig 7, along two opposite lines of 
the coelenteron, the nuclei of the endoderm lie close together, and 
here the endoderm (as far as can be made out from the longitu- 
dinal section) projects in the form of two irregular ridges into the 
coelenteron. They are, no doubt, the beginnings of the first pair of 
mesenteries. The mesenteries are thus formed at an early stage 
and before the others. The stomodaeum is quite well marked and 
its epithelium is of the same nature as the outer ectoderm. I 
have not noticed in the ectoderm of the earlier stages the pigment 
cells found in the late stage. 
I obtained several specimens of Semper’s second larva which, 
I believe, is the one named Zoanthina by Van Beneden. The 
youngest specimen (fig. 8) measured about } mm. and the oldest 
over 3 mm. in length. I have not found any specimens of this 
larva associated together in the curious manner described by Van 
Beneden — younger stages occurring within the body of an older 
stage. 
The form of the larva varies from time to time. Its usual 
appearance as it lies on the bottom of the glass vessel is that 
shown in fig. 8. Often it assumes a more elongated club-shaped 
or subcylindrical form. The colour varies ; it may be light-brown 
or dark-brown or slightly yellow, or the larva may be almost 
colourless. The colour seems to depend to some extent on the 
amount of coloured yolk in the endoderm. Light streaks running 
along the outside of the larva mark the attachments of the mesen- 
teries, which are also made evident by shallow external grooves. 
