Inheritance of Size 63 



more than two years. The means for diameters varied 

 between 30.3 and 31.0 micra, but the modes were iden- 

 tical. The coefficients of variation for diameter were 

 always large (11 to 12), as a result both of the presence 

 of parthenogenetic cysts and of the starvation treat- 

 ment. 



Entameba. Concerning many species of unicellu- 

 lar organisms there exists presumptive evidence that 

 diverse size biotypes exist, and therefore that size is 

 inherited. Thus, in the parasitic Entameba histolytica 

 (Dobell and Jepps, '18) and Entameba coli (Matthews, 

 '19) cysts were shown to differ both in mean size and 

 in frequency distribution very markedly from one hu- 

 man host to another. The cysts from several individ- 

 uals also were similar, indicating that they might 

 belong to the same one of the various biotypes. But, 

 unfortunately, the environments of these amebas may 

 have differed in such a way as to produce these very 

 size diversities, even though the distribution of sizes 

 from one host was usually normal. Ujihara ('14) 

 gathered data which tended to show that the cyst sizes 

 were not correlated with the sizes of the free-living 

 amebse in any one host infected with Entameba his- 

 tolytica. 



Colpoda. The infusorian Colpoda furnished data 

 upon the inheritance of constancy in size (Adolph, 

 '29) entirely similar to the data for Paramecium. Due 

 to the fact that a spherical cyst was formed in prepara- 

 tion for each fission, it was a simple matter to make 

 sure that all the organisms measured were physiologi- 

 cally of one age, the age of maturity. Moreover, the 

 organisms were measured while living, so that the 

 progeny of the very individuals which had been meas- 

 ured could be compared with them. Under constant 

 conditions of temperature (26.5°) and medium (an in- 

 organic salt solution and a suspension of green flagel- 



