HEREDITY AND VARIATIONS IN PROTOZOA 575 



tary complex and the argument would apparently be supported by 

 results of conjugation between individuals of each set. In the first 

 set the high division-rate would appear to be inherited; in the third 

 set the low division-rate in most cases would appear to be inherited 

 but such series invariably die. The real test is shown by conjugation 

 in the second set which results in optimum division-rates. In such 

 sets of progeny, as shown above, the differences in vitality of the 

 offspring through conjugation are due to differences in vitality of 

 the parent. With low vitality of offspring from old parents it might 

 be argued that here is an example of the inheritance of an acquired 

 characteristic whereas it is merely a matter of general vitality. 



B. Biparental Inheritance. — Through amphimixis there is a possi- 

 bility of introducing changes in the organization of a species from 

 within. The new^ amphinucleus is a new creation and its interac- 

 tion with the cytoplasm must differ from previous interactions. The 

 cytoplasm is also different in cases of merogamy and in cases of 

 conjugation. In merogamy there is a fusion of cell bodies as well 

 as of nuclei; in conjugation the old macronucleus a product of the 

 old amphinucleus, is distributed throughout the cytoplasm and 

 absorbed. As a result of the interactions of new nucleus and new 

 cytoplasm, new structures and new activities or changed activities 

 may ensue. 



While a priori such origination of variations in Protozoa is a 

 logical consequence, as a matter of fact it has been rarely observed 

 in Protozoa. Here genotypes as well as fixed and congenital varia- 

 tions usually vary little from the fluctuating variations of a species. 

 The remarkable fixity of the genot\pe is indicated by the world-wide 

 distribution of the common species, and is clearly demonstrated by 

 long-continued cultures of any given species. Vitality also is remark- 

 ably constant as illustrated by Woodruff's long culture of Para- 

 mecium aurelia, by Hartmann's culture of Eudorina elegans, or by 

 cultures of Uroleptvs viohilis in which the a^Trage relative vitality 

 of the first 12 series representing the F to F4 generations by con- 

 jugations w^as 88 per cent and the relative vitality of a recent set 

 of series representing the Fis to the F22 generation, was 85.6 per cent. 

 Here although there was an interval of six years between the two 

 sets compared, the vitality remains practically the same. 



Despite this constancy there is some unmistakable evidence of 

 variations in the Protozoa. There is also, considerable evidence 

 that has been misinterpretated as mutations. Among the latter, 

 abnormalities in reorganization may be responsible for apparent 

 mutations. Thus a bi-micronucleated, short, race of Paramecium 

 caudatum was obtained as a result of conjugation of two normal 

 individuals (Calkins, 1906). Its two micronuclei, shortened body 

 and rounded posterior end were characteristic of Paramecium 

 aurelia and the latter was erroneously interpreted as a mutation 

 of Paramecium caudatum. The aurelia characters persisted for 45 



