Size of Nucleus 177 



therefore of the total number of nuclei originally pres- 

 ent. In warm temperatures fewer cysts formed and 

 in cold temperatures more cysts formed, from similar- 

 sized individuals; nevertheless the sizes of the cysts 

 themselves were unaffected by the temperature. 



In this species it was possible to distinguish to some 

 extent the volume of the nucleus from the volume of 

 the chromatin condensed within it. In the warm tem- 

 peratures the nuclei became larger, but the chromatin 

 masses smaller. This is an instructive warning con- 

 cerning the deduction of correlations for nuclear 

 materials. Smith made no measurements of size fre- 

 quencies in nuclei or chromatin. 



In several species of Arcella, similar observations 

 were made by Hegner ('20). In the species A. poly- 

 pora the number of nuclei varied up to seven, and the 

 size of the shell increased with the number. The num- 

 ber was very closely correlated with the volume of the 

 individual, as figure 59 shows, on the assumption that 

 the volume was proportional to the cube of the di- 

 ameter of the disk-shaped shell. This was exactly the 

 situation found in Actinosphaerium. In the Arcella 

 dentata, where no more than two nuclei occurred, 

 measurements of a large population (428 individuals) 

 showed that the modal diameter for binucleates was 

 125 percent of that for uninucleates. This ratio of di- 

 ameters corresponds to a ratio of cubes or body vol- 

 umes of 197 percent; the individuals with two nuclei 

 had therefore almost exactly doubled the bulk of the 

 individuals with one nucleus. 



Growing Opalinae from the intestines of tadpoles 

 were studied by Hegner and Wu ('21) with the result 

 that the volume of cytoplasm appeared to decrease as 

 the number of nuclei per individual became greater. 

 Nevertheless the correlation of body volume and num- 

 ber of nuclei was very high. On the basis of substan- 



