Size of Nucleus 181 



had a hundred or more nuclei and each Actinophrys 

 had only one. 



Ratios in different races. The question remains 

 whether the ratios of nuclear volume to body volume 

 are similar in various unicellular species which have 

 discrete nuclei. This is far from being the case. The 

 nuclei may form 8 per cent of the body or they may 

 constitute much less than 1 per cent. 



Within a species the ratio also differs tremendously 

 among different clones. This was demonstrated by 

 Popoff ('09) by comparing the various results upon 

 Paramecium in the Munich laboratory, all the meas- 

 urements having presumably been made under similar 

 conditions. Whereas Rautmann's ('09) cultures 

 showed 15 times as much body as nucleus, Popoff 's 

 showed 48 times as much. Intermediate lay the ob- 

 servations of Hertwig ('89) and Glaser (quoted by 

 Popoff) at about 30 times. 



2. Some External Factors 



Temperature. Temperature has been said to modi- 

 fy slightly the volumetric ratio of body to nucleus. 

 Evidence on this point is contained in the data of Raut- 

 mann ('09), which are reproduced in figure 60. It ap- 

 pears that the ratio is greatest at 20° in Paramecium. 

 But the differences are only slightly greater than the 

 standard deviations within the groups measured. In 

 Stylonychia (figure 61) the same observer found no 

 significant change with temperature. In Frontonia 

 the ratio was found by Popoff ('08) to be slightly 

 greater at 25° than at 14°. 



In all species (figure 61) the absolute volume of the 

 nucleus was markedly diminished at higher tempera- 

 tures. This was the case with the bodies of the same 

 three species (above in figure 36). In view of all the 

 errors involved in the data it is safe to conclude that 



