348 BIOLOGY OF THE PROTOZOA 



ened by the chromidia problems which are associated with all of 

 these testate rhizopoda. If, as generally believed, the chromidia 

 give rise to germ nuclei, there is some chance of this hereditarily 

 important chromatin being unequally distributed at cell division, 

 for the mass of chromidia is not halved with the same precision as 

 is the chromatin of the nucleus or nuclei. Whether or not chromidia 

 are responsible the interesting fact remains that demonstrable 

 variations in organization occur with continued reproduction. It 

 remains to be determined, however, whether the variations will 

 still breed true after endogamous fertilization and reorganization, 

 or will revert to the form of the original wild individual ; then only 

 will the matter of permanency of the changed organization be 

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

 Arcella discoides, and Arcella polypora obtained abnormalities in 

 parents and offspring which he interpreted as due to environmental 

 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, S from each of the original 4 individuals. The history 

 of these 4 strains in one experiment is condensed in Fig. 168. Pure 

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

 came from the 4 individuals A, B, 0, and I). 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. 



In general, all results that are based upon physiological differ- 

 ences must be cautiously interpreted. Thus with Uroleptus mobilis 

 individuals from the progeny of single ex-conjugants may be 

 selected at appropriate periods to show marked differences in divi- 

 sion-rates. One such individual may reproduce at the rate of 17 

 divisions in ten days; another individual from the same line will 

 reproduce at the rate of 8 divisions in ten days, and a third may 

 divide at the rate of only 2 divisions. One might erroneously 

 argue that these individuals represent the sifting out of an heredi- 

 tary complex and the argument would apparently be supported by 



