120 Regulation of Size in Unicellular Organisms 



mecium; so that from figure 24 it might be taken that 

 intervening endomixis is without effect upon size. 



Erdmann ('20) made a particular study of this point. 

 Two lines of clone were kept, and after each of four 

 endomixes the sizes were measured in various popula- 

 tions. As shown in figure 35, the changes of mean size 

 at different periods were no greater than the diversities 

 among sister cultures at some one period, with respect 

 to either length or volume of the body. 



Endomixis or a similar nuclear reorganization oc- 

 curs in numerous species when protective cysts are 

 formed. The effect of intervening encystment was 

 noted in Colpoda (Adolph, '29) and the body size was 

 found to be the same before and after it (see figure 20). 



The conclusions to be drawn from the data upon the 

 after-effects of conjugation, of endomixis, and of en- 

 cystment must be purely negative. For, each popula- 

 tion whose size was measured was in reality descended 

 from a single ex-conjugant or single ex-endomictic; a 

 great number of such populations must be measured 

 before the assurance becomes great that some few of 

 the reorganized individuals did not suffer modification 

 with respect to the inheritance of size. 



Depressions. ''Degeneration" of protozoan races, 

 which is a term meaning that the fission rate is pro- 

 gressively decreasing, has been noticed by many ob- 

 servers to accompany decrease of body size in succes- 

 sive generations. Maupas ('88) was the first to meas- 

 ure the sizes at intervals during the progressive failure 

 of his cultures. In the case of Stylonychia pustulata, 

 the length of the body shortly before the death of the 

 last individuals of the race was only one-fourth of the 

 original length. 



"Rhythms" which have not been identified with en- 

 domixis have been studied in relation to size in a few 

 instances. Woodruff ('13) found in continued cultures 



