156 0)1 the Genetics of the Ciliate Protozoa 



The karyoplasmic ratios f -^j calculated for these three temporatiires 



are respectively 807, 77'4, 74. The dimensions of the micronuclei in 

 Fruntonia appear to vary like those of the meganucleus (Popofif, 1909), 

 but in Stylonychia they were not studied. 



68. These size-differences are not permanent ; apparently they are 

 manifested as a direct resjjonse to temperature — like differences in rate 

 of fission (§ 55). Rautmann (1909) has found, however, that ri.se of 

 temperature, rise of fission-rate, and rise of karyoplasmic ratio do not 

 all run parallel. For increase in rate of fission (in Paramecium) 

 accompanies increase in temperature — the temperatures tried being 



5° to 35° C. : whereas the karyoplasmic ratio f-v^j increases with the 



temperature up to 25°, but then begins to sink. When an organism 

 is subjected to a change of temperature, it can regulate its karyoplasmic 

 ratio to that characteristic for the new temperature in the space of 

 time which elapses between one division and the next — for a tem- 

 perature interval of 5° C. 



69. Jollos (1913) experimenting with pure lines of Paramecium, 

 cuudatum, has found that although differences in size are produced by- 

 changes of temperature — as described by Hertwig, Popofif and Rautmann 

 — nevertheless these differences are transitory. At a new temperature, 

 a change of size is at first observable, but later it disappears. The 

 animals appear to become adapted to the new temperature and then 

 to readjust themselves to their original proportions. Jollos also states 

 that resistance to extremes of temperature can be induced in Para- 

 mecium to a slight degree. But here again the modification is 

 impermanent — being lost if the organisms are returned to a normal 

 temperature. 



70. In one case Jollos (1913) claims to have produced a permanent 

 change (" mutation ") in Paramecium. From a race subjected to a high 

 temperature he obtained a small race which is permaveutly small — at 

 high, normal, and lower temperatures. This race has conjugated without 

 reverting to the original size. It differs also in being less susceptible 



