HEREDITY AND VARIATIONS IN PROTOZOA 573 



will the matter of permanency of the changed organization be 

 settled. Jollos (1924) exercising selection in Arcella vulgaris, 

 Arcella discoides, and Arcella ixjlypora obtained abnormalities in 

 parents and offspring which he interpreted as due to en\'ironmental 

 conditions especially to the accumulations of metabolic waste. 

 With cultivation under better conditions of the medium such abnor- 

 malities gradually disappeared with reversion to the normal. 



Further evidence of the sorting out of mixed characteristics was 

 given by Calkins and Gregory (1913). The first 4 of the individuals 

 formed by an ex-conjugant of Paramecium caudatum were individ- 

 ually isolated and the history of their progeny was followed out in 

 32 pure lines, 8 from each of the original 4 individuals. The history 

 of these 4 strains in one experiment is condensed in Fig. 235. Pure 

 lines that died are indicated by X and the 4 sets of 8 lines each 

 came from the 4 individuals A, B, C, and D. Physiological differ- 

 ences in the progeny of these 4 are indicated by the division-rates 

 and by the ability to conjugate, the progeny of A for example giving 

 epidemics of conjugation at each test while similar tests gave no 

 conjugations in the progeny of B, C, and D until nine months of 

 culture and then in very small numbers. Similar variations in size 

 were characteristic of the different quadrants. It is possible that 

 such results are due to the segregation of germinal materials during 

 three metagamic divisions of the amphinucleus, each of the original 

 four cells receiving a different combination of macro- and micro- 

 nuclei. 



Selection on the basis of physiological activities alone is not 

 always satisfactory in results. Middleton (1915) for example, con- 

 tinually selecting progeny of Stylonychia for rapidity and slowness 

 of division obtained two sets with what he regarded as an inherited 

 difference in rates of division and the permanence was tested by 

 conjugation— the ex-conjugants being followed for fifteen days. 

 "Thus," he concludes, "it is clear that the heritable difference in 

 fission-rate brought about by selection during vegetati^•e reproduc- 

 tion is not lost when the animals conjugate, but persists through 

 that ordeal" (1915, p. 497). Not only was the period of observa- 

 tion of ex-conjugants too short for a conclusion of such importance 

 but the actual results justify an opposite conclusion. From his 

 table we learn that 60 ex-conjugants from "fast" lines divided 

 1297 times in fifteen days, while 60 ex-conjugants from "slow" lines 

 divided 1310 times during the same period. That is, his carefully 

 selected slow lines after conjugation actually divided more times 

 than did the selected fast lines. His remarkable conclusion was 

 apparently based on the fact that on 3 of the 5 three-day periods 

 his fast lines divided a little more rapidly than did the slow lines 

 but not fast enough to overcome the lead obtained by the slow lines 

 during the first two periods. 



