supporting lamella

514 W. B. HARDY.
fragments may sometimes be seen; and further because the
muscular elements are absorbed for some little space about the
point where the rupture takes place (figs. 7 to 10).
The tongue of endoderm-cells rapidly becomes a tubular
outgrowth, and the cells at its apex lose their nutritive
spheres and become small, dense, on the whole ill-staining
cells.
At this stage it is perhaps impossible to distinguish the limit
between ectoderm and endoderm, while at the same time a
fusion of cell substance has taken place (fig. 10), so that we
have a stage closely resembling the blastema which gives rise
to the bud as described above.
Fig. 10 represents this stage, and is an accurate drawing,
made with the aid of a camera lucida, of a preparation
from a specimen killed with corrosive sublimate and stained
with picro-carmine; the whole specimen being remarkable
for the good preservation and clear definition of its
histological elements. The section figured passes rather
obliquely through the young gonophore, but the next in the
series shows that the primitive germ-cells have now travelled
in under the superficial columnar cells of the ectoderm to form
a cap for the fused ectoderm and endoderm.
The next stage to be noticed is in many respects remarkable.
By a fresh formation of supporting lamella the whole bud with
its contained germ-cells becomes separated from the maternal
tissue, while at the same time a fold of supporting lamella becomes
formed which separates the ectodermal elements with
the primitive germ-cells from what is usually known as the
endoderm lamella (fig. 11). The endoderm lamella, therefore,
from this time onwards, is separated from the endoderm
of the parent by a well-defined and permanent supporting
lamella; and it is noticeable that up to this stage and until
they degenerate the cells of the endoderm lamella are not of the
ordinary endoderm type, but resemble in every detail
the ectodermal cells of the gonophore. 1
1 The columnar cells of the maternal ectoderm remain undisturbed and
unaltered by these various changes. I regard them as belonging to the