supporting lamella

HISTOLOGY AND DEVELOPMENT OP MYRIOTHELA PHRYGIA. 529
protoplasm. Such cells form a very striking feature of osmic
acid preparations. The fluctuations in the size of the individual
cells in the endoderm of the blastostyles naturally leads to a
corresponding fluctuation in the total bulk of that tissue. In
specimens taken in May or June it sometimes almost fills the
cavity of the blastostyles.
We therefore have in the blastostylar endoderm, in addition
to the scattered gland-cells, the following:—(1) Small dense
cells with nucleus and nucleolus which stain deeply. (2) Cells
•whose protoplasm is completely occupied by vacuoles, each of
which, some of which, or none of which contain nutritive
spheres. And there are numerous intermediate stages between
(1) and (2), with either a small or a large portion of the cell substance
occupied by vacuoles. The protoplasm of cells (1) and
(2), or of the intermediate stages, appears in osmic acid preparations
to be remarkably dense and almost glassy, and the vacuolation
is limited to the large vacuoles which embed the nutritive
spheres. But other vacuolate cells occur, forming a third
class, whose protoplasm is not of this character, but is so
occupied by vacuoles of all sizes as to give the whole cell a
very characteristic appearance (fig. 22). The vacuoles always
differ in size in different parts of the cell, being larger near the
free surface where they may contain young nutritive spheres.
These cells, forming the third type of vacuolate cell to be seen
in sections through the blastostyle, may be regarded as cells
which are actively forming nutritive spheres.
Before considering the processes going on in the vacuolate
cells generally, it will be well to turn to the nutritive spheres
themselves. The endoderm generally contains three kinds of
formed bodies—that is to say, bodies which are not of the
' nature of material merely ingested by the cells, but rather are
new formations resulting from the activity of those cells.
Ofthese the most common are small spherical bodies, generally
about 3 JU in diameter. These crowd the endodermcells
in great numbers, but are always most numerous in the
foot and blastostyles. They stain uniformly, but not so deeply
as to become opaque, with osmic acid, and when perfect appear
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