ABSTRACT
A very thorough knowledge of the nuclear phenomena in an organism so largely employed as is Amoeba proteus by investigators in many branches of science, no less than by teachers of biology, is greatly to be desired. That there are, at present, gaps in this knowledge is quite evident from an inspection of the literature. One such gap was responsible for a question asked of me by Professor Grégoire while I was working in the Carnoy Institute, Louvain, in 1924. This question emphasized the fact that, in my paper on ‘Nuclear Divisions in A. proteus’, I had, as had Doflein (8) before me, left it open whether or no the portions of the karyosome which stain more deeply than the rest consist of chromatin. When reading over the manuscript of my paper Professor Graham Kerr had said that he saw no reason for their not being chromatin, while fully sympathizing with my reluctance to decide the question from observation made on the nucleus of the adult. Griiber (11) had no hesitation in describing these portions of the karyosome as ‘chromatin-containing’? While I was working out the phenomena connected with the formation of encysted young, the karyosome of the fully mature individual had appeared to me to be nothing more than a portion of the nuclear reticulum where the meshes were not quite so large as in the surrounding areas. In contradistinction to this condition was that which obtained in those young A. proteus which I had been able to examine before the publication of my paper (25, p. 137, Text-fig. 10) and of which a preliminary account was given. In these the karyosome appeared much more solid and less reticulate, being quite the most conspicuous structure in the nucleus.
In most of my previous work on A. proteus, as well as in this present paper, I have made little reference to papers published before 1916 because it is not always possible to be quite sure which of the two large free-living amoebae is referred to in the said papers. In the case of Griiber (11), however, it is quite easy to see from his figures that he worked on the same amoeba that I have used, i.e. the A. proteus of Pallas (Leidy). In view of the recent work on Protozoan nuclei by Bëlàr (1) it may be well to remind the reader that in 1916 Schaeffer (19) showed, quite conclusively, that two distinct species of amoebae had hitherto been called A. proteus, viz. (a) the true A. proteus Pallas (Leidy) and another (&) which he named A. dubia (Schaeffer). (See also Carter (3).)
I have sent cultures of A. proteus to Kansas, where they arrived in good condition. Professor Schaeffer has informed me that these amoebae differ in no respect from those he obtains in America.
In his recent monograph on amoebae (20) Schaeffer suggests that these two free-living amoebae should be placed in the genus Chaos, and that A. proteus should henceforth be known as Chaos diffluens.
Bëlar (1) has evidently not consulted the work of Schaeffer (19) and Carter (3). His descriptions are therefore vitiated by the fact that he has not made clear to his readers which of the two large free-living amoebae he has used. The figures which he gives on p. 296 are those of A. dubia, not A. proteus.
His want of knowledge of this fact may also be responsible for his statements on p. 560, that my observations on the division of the nucleus in A. proteus can be dismissed, because made on pathological material. I should suggest to him that before making a priori statements he should verify the accuracy of the figures in Pl. 2 (24). Such an investigation on his part would reveal to him the highly refractory and unaccommodating character of A. proteus (= Chaos diffluens), and its quite unsuitable character for inclusion into the beautiful schemes shown on p. 538 of the same work (1).
