560 Dr. M. Hartog. [ Dec. 1, 
with its centres joimed up by consecutive spindles (fig. 8). The higher the 
permeability of the chains, the greater the reluctivity of the medium, the 
more nearly could we approach an equilateral triangle; as it is, in the cell 
triaster as figured by many observers the three centres are rarely, if ever, 
equidistant. . 
Again, we can obtain a tetraster with four consecutive spindles and a fifth 
spindle uniting two opposite centres, like that often found involving four 
nuclei in the embryo-sac of Flowering Plants, by using two unlike poles 
alternating with two cores (fig. 9). This figure is clearly the preceding 
triaster doubled, or, as we may say, united with its “reflection.” We can 
obtain the equivalent of four triasters joined into a square, if we place 
four alternate poles at the angles, and a core in the centre (fig. 10). 
Either of these two figures can by addition of suitable centres be extended 
indefinitely to “fill space.” Thus, if we replace the term “pole” by 
“centre” both of Rhumbler’s dicta fall to the ground: the physical explana- 
tion is obvious, and there is no jugglery. It would appear that in the cell, 
when there is a plurality of centres, they tend to acquire charges such that the 
number of spindle-connections is a maximum.* 
XII. 
The tetraster, which occurs, for instance, in the spore-mother-cells of the 
Hepatice, where four centres occupy the poles of a tetrahedron, and the 
spindles extend only to a central mass of chromosomes, may be modelled in 
a plane by a set of three “like” poles surrounding a central core or an 
opposite pole (or by a single central pole and three cores, which, of course, gives 
a weaker field). The addition of a fourth “like” pole vertically above 
the core would complete the model, supposing that the core could also rise to 
the centre of the figure, drawing up with it its three spindles. Or we may 
model the tetraster in a plane with four “like” poles and a central core or 
“unlike” pole to represent the aggregated chromosomes, or a central pole 
and four surrounding cores (fig. 11). The chromosomes are highly permeable 
to mitokinetic force (see below, p. 564). 
XIII. 
We can study and elucidate other cell-figures by the aid of models. Thus 
Vejdowsky and Mrazek have found that one or both of the centrosomes may 
be drawn out into a spheroidal “ blob” on the side next the attachment of 
the spindles—a state of things evidently due to the opposite actions (@) of 
the spindle under mitokinetic force, and (0) of the tractive forces in the 
cytoplasm pulling the centrosomes towards the periphery of the cell (fig. 4). 
* This point will be further discussed in Part IT. 
