488 



JENNINGS— HEREDITY IN PROTOZOA. 



April 24, 



Table XXIII. 



Comparative Sizes in Microns of g and i and their Progeny at Different 



Dates, when Cultivated under the Same Conditions. 



It will be recalled that in the original culture from which came 

 g and i, there was a still larger set which we called E. Ten of these 

 were selected and cultivated under the same conditions as g and /. 

 They retained throughout their much larger size (numerical results 

 are given later), so that from this culture we have isolated three 

 lines or races which retain their differences in size under the same 

 external conditions. 



At this period, then (January i, 1908), I had in the laboratory a 

 number of lines or races which had been studied with care. These 

 formed two sets, so far as our knowledge of them up to this point is 

 concerned. The two lines, D and c, from culture /, were clearly 

 distinct even under identical conditions. The three lines, g, i and E, 

 from the second wild culture 01, are likewise clearly distinct from 

 each other. But the relation of g, i and E to D and c is uncertain ; 

 we may have on hand five distinct lines, or only four, or three. 



To determine whether any of these five lines are identical, it is 



necessary to cultivate all five under the same conditions. A certain 



number must be selected from each ; these must be brought into the 



same culture fluid and allowed to multiply in the same environment. 



It is extraordinary what difficulties are presented in carrying out this 

 apparently simple plan. The different lines have become adapted to certain 

 diverse nutritive conditions; if now they are brought at once into the same 

 culture fluid, some of them die. In the present case, g and i had been living 

 in comparatively fresh hay infusion, D and c in different old hay cultures, 

 £ in a culture of decaying pond weeds. When all were brought into fresh 



