Races of Paramecium. 553 



races of various sizes, and that what the author did was to iso- 

 late a representative of a small race. Certainly this would be the 

 explanation in the case of Paramecium, and in the account as 

 Popoff gives it there is absolutely no proof that the small race 

 was derived from one of different size. 



2. The second case is that of a Stentor from the same culture 

 but somewhat above the usual size; this when isolated gave prog- 

 eny above the usual size (p. 145-147). Here again we have a 

 culture which is not said to have come from one individual; 

 the author does not know the size of the ancestors of his large 

 race; he did not isolate the two products of the supposed unequal 

 fission and observe that they gave races of unequal size. There 

 is thus no proof whatever that the large race had arisen from one 

 of a different size. If the original culture, like a wild culture of 

 Paramecium, contained races of varying size, this gives a full 

 explanation of all the facts as Popoff states them. 



3. The third case is in Frontonia leucas (p. 147-148). Here 

 the facts are in almost every detail parallel with those of cases 1 

 and 2 in Stentor. The original culture is not said to have been 

 derived from a single individual. On November 11, large and 

 small specimens were isolated, but these are not said to have 

 come from the fission of a single individual. Their progeny re- 

 tained the relative sizes of the parents, showing that they belonged 

 to different races. The facts can be readily paralleled in any 

 "wild" culture of Paramecium — but the explanation is that 

 di\ erse races were present in the culture from the beginning. 



(Popoff in the text speaks of the small specimen as "Eine durch 

 ungleichmassige Teilung entstandene, auffallend kleine Fronto- 

 nia" (p. 147), but again his extract from his note-book on the 

 same page, indicates clearly that the idea that this specimen 

 came from unequal division was an assumption, based on his 

 general theory. The note-book says merely "11. XI. 07. Die 

 Kultur mit einem sehr kleinen Tier angelegt." So important a 

 point as the exact observation of its origin would surely not have 

 been omitted. In any case, the author had no knowledge of the 

 normal size of the line of individuals from which this small speci- 

 men came.) 



