The role of the nucleus in the locomotion of an entozoic ameba.

Abstract

There is a large ameba, oval or circular in cross section, entozoic in the rectum of the bull-frog tadpole, which averages well over 100 μ in length, and from one-fifth to one-fourth as wide as long. It is strikingly peculiar in that it possesses an axial stream which flows swiftly and uniformly toward the anterior end, from which it is reflected about itself as a hollow cylinder of protoplasm either flowing posteriorly or remaining stationary with respect to particles on the substratum, depending on whether the ameba as a whole is “marking time” or moving forward. The large conspicuous nucleus always lies in a crescentic zone of clear ectoplasm at the extreme anterior end of the ameba, so that its posterior surface appears to be contiguous with the endoplasm.

That the nucleus plays a definite rôle in directing protoplasmic streaming, and thus possesses potentialities which influence strongly the shape of the ameba and the direction and manner of its movements is suggested by the following observations and experiments.

1. It can be observed that the nucleus oscillates from side to side in the anterior end of the ameba (though not in one plane as it appears to the observer through the low powers of the microscope). The endoplasm flows into the portion just previously occupied by the nucleus, the nucleus moving (presumably being forced) to a new position, into which the endoplasm immediately follows it. The process is steady and continuous. Thus the nucleus and anterior tip of the ameba both describe spiral paths.