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