CELL SIZE AND NUCLEAR SIZE 49 
not practicable to measure them directly with the 1/1 micrometer 
eyepiece. Nevertheless by selecting sections in which only a 
part of the chromosomes are shown I have been able to sketch 
the outlines of many of them with what I believe to be substan- 
tial accuracy. For the purpose of comparing the sizes of chromo- 
somes from different cleavages I have chosen two generations of 
blastomeres in which the difference in the size of the nuclei is at 
a maximum, the nucleus in one cell being about twice the di- 
ameter of that in the other; these blastomeres are the macromeres 
AB and CD, and the micromeres ja-—/d (figs. 7 and 8). In the 
former the diameter of the nucleus just before division is about 
24u, in the latter about 144. When the nuclei of the cells in 
question had begun to divide and the mitotic figures were in the 
equatorial plate stage, the chromosomes from a number of these 
spindles were drawn as accurately as possible with a camera 
lucida. In order to be certain that the stage of division was the 
same in each case only longitudinal sections through the spindle 
were chosen; and in order to avoid as far as possible individual 
differences in the sizes of chromosomes, only the largest and most 
isolated chromosomes were drawn. Fig. 9 shows chromosomes 
from four different spindles of the second cleavage; fig 10 shows 
chromosomes from the first division of the first quartet cells 
(1a—1d), also from four different spindles. In all cases the chro- 
mosomes are magnified 2000 diameters. 
It is plain from these figures that the chromosomes from the 
larger nuclei are larger than those from the smaller ones, though 
the difference in the diameters and volumes of the chromosomes 
are not as great as the difference in the volumes of the nuclei 
from which they came. The average volume of the chromosomes 
from the large nuclei is about 5.2 cubic w and of those from the 
small nuclei about 2.6 cubic yu. While the volumes of the nuclei 
as a whole are to each other about as 5 : 1, the volumes of their 
individual chromosomes are to each other as 2:1. In the case of 
nuclei which differ but slightly in volume it is not possible to be 
certain that the chromosomes differ in size, but in all cases in 
which the differences in the size of nuclei is considerable it can 
THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 12, No. 1 
