supporting lamella

HISTOLOGY AND DEVELOPMENT OF MYBIOTHELA PHRYGIA. 511
concerned in the manufacture of nematocysts (fig. 4). In
some sections scanty patches of small cells similar to those
described above may be seen, but they are now the exception
and not the rule. On the other hand, over considerable
regions the ectoderm may be even more decrepit than that described
above, for even the columnar cell layer may be imperfect,
while the basal cells are represented largely by irregular
spaces. On the other hand, the muscular layer and supporting
lamella are proportionately better developed. Measured from
the external surface of the cuticle to the external surface of
the supporting lamella the ectoderm at this period is from 30
to 35 fi in thickness.
We thus see that as the season advances and the reproductive
period comes to a close the ectoderm of the gonophore-bearing
region becomes more and more exhausted of those small cells
which are such a characteristic feature of it in the spring, and
I think there can be little doubt that their disappearance is
connected with the active formation of gonophores during the
summer months.
So far I have spoken of them merely as the small cells of the
proximal ectoderm. It is necessary to see whether these cells
are all alike, or whether they may be divided into one or more
sets differing in their function and connections. In tracing
the process of formation of the nematocysts I have said that
they first appear as a rounded hyaline mass embedded in the
protoplasm of a cell which then lies in the deeper part of the
ectoderm.
The smallest cells containing these masses may be only 10p
in diameter ; but though they do not differ markedly from the
bulk of the small cells in point of size, they do differ in one
very important particular, namely, in the fact that they are
always connected by a delicate process with the nerve network
(fig. 5).
On the other hand, we have in addition to these small cells
which are in connection with the nerve network, and so often
contain some trace of a developing nematocyst, other still
smaller rounded cells, which appear, even with the highest