THE PEOBLEM OF MITOSIS. 
577 
since tin’s is not seen in the mitotic triaster, correspondence 
is incomplete. In dealing with Hartog’s interpretation he 
repeated that the theory of unlike poles is disproved by 
triasters ; for, in the figures obtained with the iron core, one 
spindle must always be formed more strongly than the other 
two, and an equilateral triaster, such as occurs in Echinoderm 
ova, can therefore never be obtained. He showed, moreover, 
that the figure produced by the charcoal iron balls differs 
from mitotic triasters in that spindle axes are straight in the 
latter and bent in the former. Furthermore, he pointed out 
that in magnetically produced tetrasters having one diagonal 
spindle, the last-named must lie in the long diagonal, i . e . 
between the two real poles ; whereas in mitotic tetrasters it 
lies in the short diagonal, as is shown in his figures and those 
of 0. and R. Hertwig. He then described two tetrasters with 
two diagonal spindles, obtained from sections stained with 
htematoxylin and light green, and superior to his older whole 
preparation; and thus again contradicted Hartog’s denial of 
the existence of such figures in mitosis. With regard to 
contraction theories, he remarked that we know nothing con- 
cerning the nature of the rays ; and said that the crossing of 
spindles, as observed in tetrasters, is explicable on the 
assumption that rays are either independent fibres or mutually 
dependent portions of a figure representing lines of force, 
because crossed rays have been found by Rhumbler not to lie 
in the same plane. 
Closely following these criticisms, a paper appeared by 
Lawson upon the achromatic figure in vascular plants. In 
this he said that changes undergone by the cliromatin during 
the prophase of mitosis cause the karyolymph gradually to 
diffuse by exosmosis through the nuclear membrane; and this 
diffusion is said to be the direct cause of diminution observed 
in the nuclear vacuole. He believed that the corresponding- 
increase in volume of the cytoplasmic portion of the cell 
cavity involves a change of tension resulting in readjustment 
of the reticular structure, and that portions of the last-named 
immediately surrounding the nuclear vacuole' are drawn out 
