MUSEUM OF COMPARATIVE ZOÖLOGY. 137 
characteristic of the resting nucleus as of the mitotic nucleus, was 
postulated by Rabl (’85, p. 323) from a careful study of the chromatic 
network in the “skein stage ” of mitosis. In a recent paper (’89, pp. 23, 
24), the same writer states that the “polar depression,” usually visible 
in young daughter nuclei, persists much longer than usual in the epi- 
thelial nuclei of the Triton ; so that for these mitotically dividing nu- 
clei it is highly probable that polar differentiation is always present in 
the resting state. Carnoy (’85) has shown that, in the resting nuclei 
of the testicular cells of certain Arachnids, the chromatic filaments are 
distinctly arranged with reference to a definite axis (Planche V. Figs. 
165-169), and Van Gehuchten (’89) has found the same in glandular 
cells of a Dipterous insect, Piycoptera contaminata. 
It is obvious that the discovery of an “organic axis,” as Van Gehuch- 
ten calls it, in amitotically dividing nuclei is more difficult, for here there 
is no polar depression or longitudinal arrangement of chromatic fila- 
ments to indicate its direction in the resting nucleus. It is usual for 
each division of the nuclei of the serosa to take place at right angles, or 
nearly so, to the plane of the previous division. This is well seen in 
many multinuclear cells,,where one or both pairs of nuclei lie trans- 
versely in the cell, and therefore at right ‘angles, or nearly so, to the 
direction of the first division (see cells 2 and 3, Fig. 14). In other 
cases, however, two consecutive divisions take place in the same direc- 
tion (Fig. 14, cell 2). It occurred to me that possibly there was an 
organic axis in the nuclei of the serosa which in some cases exerted a 
controlling influence upon the direction in which division took place, 
but which in most instances was counteracted by influences resident in 
the cytoplasm. Transverse divisions of the nucleus (Fig. 12) could then 
be accounted for by assuming that the influence of the organic axis is 
dominant in these cases, while oblique divisions would be explainable on 
the ground that neither influence was predominant, but that both acted 
with about equal force in directions at right angles to each other. A 
question of interest in this connection is, whether, when the cytoplasmic 
influence is dominant, and tends to make the nucleus divide in a plane 
parallel to its organic axis, division actually does take place in that 
direction. If such were the case, an organic axis would be a fact of 
slight morphological importance, and the longitudinal arrangement. of 
chromatin, which takes place in the earlier stages of constriction (Figs. 
4, 6, 7), might occur in any direction, without reference to an organic 
axis. If, on the contrary, it were necessary that the longitudinal fila- 
ments should be arranged parallel to the organic axis, in order that 
