supporting lamella

524 W. B. HAEDT.
body. In Myriothela they occur in their greatest abundance
in the endoderm of the lower half of the tentacle-bearing
region. Bat they are also numerous in the middle region of
the body whence the blastostyles spring, and may even occur in
limited numbers in the endoderm of those structures near their
points of attachment.
In the middle and lower regions of the body the endoderm
is to a certain extent different from that already described.
The villi, as a rule, become less muscular, while at the same
time their apical cells change their characters and become more
and more akin to the vacuolate cells. The endoderm of the
body-wall from which the villi spring, and which in the lower
tentacle-bearing region is composed of cells in no wise distinguishable
from those lining the villi, changes its character
in the blastostyle-bearing region. There it is composed of
long columnar cells, each with a single nucleus, and each
composed of dense well - staining protoplasm free from
vacuoles.
The endoderm maintains these characters in the foot; that
is to say, the villi, which here are of the nature of broad flangelike
folds, are covered by vacuolate cells with rarely a glandcell,
while the endoderm of the body-wall is composed of the
deeply-staining columnar cells. At the extreme end of the
animal, however, the supporting lamella ceases to exist, and to
a certain extent the limits between ectoderm and endoderm
become obscured, and a kind of growing-point to the creeping
stolon is the result.
The endoderm of the blastostyles will receive special mention
later. To make this general account of the whole endoderm
complete, however, I will merely state here that the villi in
the blastostyles are low conical structures almost exclusively
composed of vacuolate cells. A few gland-cells lie scattered
in the proximal third of each blastostyle.
Taking the most general view of the structure of the epithelium
lining the enteric space of Myriothela as described in
the preceding pages, we see that it may be divided into different
regions. These are—(1) An oral region characterised by the