igos.l JENNINGS— HEREDITY IN PROTOZOA. 505 



differential action of the diverse environments lasted but a short 

 time. (2) The experiments were directed toward determining 

 whether the differences produced were permanently inherited. Crit- 

 ical investigations have not yet been made to determine whether the 

 environmental eft'ects may not persist for one or a few generations 

 after transference to the new fluid; nor whether long continued 

 action of a certain environment may not produce more lasting results 

 than brief action. 



To these points I hope to devote special and extended investiga- 

 tions. The purpose in the present paper is to show on this matter 

 the main general result; this unquestionably is that environmental 

 action is not as a rule inherited in any lasting way. 



(&) Selection from Among Differing Individuals in tJie Same 



Environment. 



Besides the differences among individuals under different envir- 

 onments, we likewise find differences among individuals of the same 

 pure line in the same culture, as a glance at the tables of the appendix 

 will show. What will be the effect of selecting for breeding larger 

 and smaller specimens from such a culture, avoiding, so far as pos- 

 sible, different stages of growth? 



In order to make the selections properly, certain things must be 

 considered. ( i ) It is well to bring the culture into as stable a con- 

 dition as possible — a condition where there is little or no multipli- 

 cation — in order that we may not be confused by different stages in 

 growth. (2) It must be remembered that, so long as conjugation 

 does not occur, the same results that selection would produce are 

 brought about in the ordinary course of events, save that the large 

 and small specimens remain mixed. That is, if there is congenital 

 variation, producing large and small individuals, this must occur in 

 the same way whether the dift'erent sizes are isolated or not. The 

 progeny of every individual forms a " pure line," quite unmixed with 

 any other, so long as no conjugation occurs. If, then, by variation 

 a large individual a and a small one b are produced, and these differ- 

 ences are inherited, then later we shall find a mixture of two strains 

 instead of a single strain. We should then expect the progeny of a 



PROC. AMER. PHIL. SOC. XI.VII. I90 GG, PRINTED JANUARY 12, I909. 



