If the ectoplasm is actually endoplasm that has passed into the gel
state, then the honeycomb condition just described resembles an
intermediate stage where only a part of the endoplasm has been
transformed. This network of endoplasm is strong enough however to
impede the flow of the main stream of endoplasm along the sides of the
pseudopod; but when large objects, such as the nucleus or food masses,
too large to be readily carried in the endoplasmic stream, impinge
against the imperfectly solidified sides of the tube of ectoplasm, the
innermost strands of the spongy network of ectoplasm snap, usually with
readiness, allowing the large object to pass by.
The surface of a young pseudopod is smooth, a cross section being oval
in shape (Figure 3, _a_); but as the pseudopod increases in size, large
folds or ridges begin to make their appearance. Usually the first ridges
to appear are lateral. They begin as small waves of hyaloplasm which
flow out along the sides of the pseudopod for a short distance and then
continue to move forward. The endoplasm then flows in a number of small
parallel streams amid numerous obstructions through the ectoplasmic tube
of the pseudopod into the wave of ectoplasm. After the ridge is well
begun, there is frequently observed a slow forward-moving stream of
endoplasm within it, but the ridge is never closed from the main
endoplasmic stream, as is readily proved by the numerous small streams
of endoplasm which continually filter through the ectoplasm into the
ridge.
In addition to the lateral ridges, which, as stated, are usually formed
first, there appear ridges on the upper side of the pseudopod as well,
and presumably also on the under side. So far as could be determined
these ridges are all formed in much the same way; that is, by the
projection of a small wave of protoplasm from some part of the surface
of the pseudopod. The ridges do not always grow by extension at the
anterior end as described above. Not infrequently a ridge ten to twenty
times as long as wide is pushed out along its whole length at once. This
is especially likely to happen in a slender pseudopod that suddenly
becomes the main pseudopod. The width of a ridge, especially on the
upper surface, does not change much after formation. One can frequently
find two or three ridges of about the same width, which run the whole
length of the ameba with the exception of a short distance at the
anterior end, where, as before stated, there are no ridges.
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