410 
Mr Menon, Notes on Semper' s Larvae . 
mesenteries, on account of the presence of these cells, form most 
conspicuous structures in transverse sections. The cells of the 
mesenterial filaments agree with those of the lining of the stomo- 
daeum. The filaments consist of radially arranged, elongated 
cells and have a rounded outline. 
The youngest stage obtained of Zoanthella was a sterrogastrula 
of about 1 mm. in length. It had a vermiform body with rounded 
ends, and was slightly bent towards the ventral side. In addition 
to the covering of small cilia there was the characteristic longitu- 
dinal band of long cilia. It had a yellowish colour with irregular 
dark brown patches (fig. 4). 
In this stage there is a circular mouth placed at one end of 
the body. A section of this stage is shown in fig. 5. The ectoderm 
is a well-defined layer, and consists of radially arranged columnar 
cells. Besides the ordinary cells, cells with granular contents and 
nematocysts are also present. The nuclei which are round or 
elongated are arranged in the outer and middle parts of the ecto- 
derm. Below this nucleated laj^er there is a zone which remains 
uncoloured in stained sections. On the ventral side of the trans- 
verse section there is a shallow groove which lodges the long cilia. 
At the bottom of the groove the nuclei are round and lie close 
together. 
The ectoderm is separated from the inner mass by a thin, 
structureless lamella. This lamella is very thin throughout and 
in the region of the ciliated band appears to be almost absent. 
Within this mesogloea there is a syncytium which completely 
fills up the interior of the gastrula. The syncytium contains 
numerous scattered nuclei, } r olk spherules and large and small 
vacuoles, some of which are in the living larva filled with fat 
globules. The vacuoles become larger towards the mouth. Imme- 
diately below the mouth there is a shallow quadrangular space 
into which the mouth opens. The space is lined by a continua- 
tion of the ectoderm, and is thus a short stomodaeum. The colour 
of the larva seems to be due to the coloured globules in the inner 
mass. Whether this syncytial mass has been developed secondarily 
from the simple wall of a coeloblastula as in Manicina , or, as seems 
more probable, is the inner portion of a solid morula the outer 
cells of which became differentiated to form the ectoderm, pannot 
of course be decided till the earlier stages are examined. 
The definitive endoderm is formed from the syncytium in a 
manner which has been described for Manicina , Ceriactis , and 
other genera. This is well seen in an older larva of which a 
section is represented in fig. 6. The ectoderm does not differ 
from that of the preceding stage. The mesogloea remains very 
thin. Neither here nor in the earlier stage is there any folding 
of the mesogloea to indicate the commencement of a mesentery. 
