NUCLEAR VOLUME AND LIFE-CYCLE OF HYDATINA 291 



have measured the nuclei and cj^toplasm with a planimeter in 

 accordance with the method described below, in order to discover 

 more precisely the grounds for this conclusion. The results, 

 stated in simple averages for all of the cells in each figure, are 

 as follows. 



A parthenogenetic female Moina, taken from an early genera- 

 tion after the fertilized egg and from a culture at high temperature 

 (Papanicolau's fig, 1), which should for both of these reasons 

 have a small Kernplasmarelation, shows a ratio of nuclear area 

 to cytosomal area of 0.229. In his figure 2 are similar cells from 

 a parthenogenetic female likewise from an early generation, for 

 which reason the Kernplasmarelation should be small; but this 

 female was reared at room temperature, hence the nuclear volume 

 should be relatively somewhat greater than in figure 1. The 

 ratio of nuclear area to cytosomal area in this figure is 0.231. 

 Papanicolau's figures 3 and 4 represent, respectively, a partheno- 

 genetic and a sexual female from a middle period of the life- 

 cycle. Presumably both of these should show a larger Kern- 

 plasmarelation than either figure 1 or figure 2 and that of figure 4 

 should be greater than that of figure 3. The measurements show 

 the relative nuclear area to be 0.354 in figure 3 and 0.351 

 in figure 4. 



In his fig-ure 5, which is from an early generation, but from a 

 starved animal at room temperature, and which should have 

 relatively larger nuclei than figures 1 and 2, though perhaps not 

 greater than figures 3 and 4, the ratio K/P is found to be 0.312. 



His figures 6 and 7 are from intestinal cells of Simocephalus, 

 the two specimens differing in that the former is from a somewhat 

 earlier period in the life-cycle than the latter, and the first was 

 reared at room temperature, the second at low temperature. On 

 both these counts figure 7 should show a larger Kernplasmarela- 

 tion than figure 6. The actual ratios indicated by measurement 

 are 0.175 for figure 6, 0.209 for figiu'e 7. 



With one exception the differences in these figures are of the 

 kind assumed by Papanicolau, though in one instance the dif- 

 ference is very small. Whether any of the differences are signifi- 

 cant cannot be determined statistically, since none of the figures 



