,9o8.] JENNINGS— HEREDITY IN PROTOZOA. 497 



It is clear, then, that the question placed at the head of the 

 present section is to be answered in the negative. The diverse lines 

 of different size are not merely different stages in the life cycle. 



(c) Other Evidences of Permanent Differentiation in Sice, Inde- 

 pendent of the Life Cycle. 

 The proof just given, that lines beginning with conjugants are 

 dift'erentiated in size even in the same portion of the life cycle and 

 under the same conditions, is conclusive. But it may be worth while 

 to give briefly certain other evidences of the same thing. 



1. First we have the fact that in a given culture the conjugants 

 themselves dift'er in size ; this has already been shown by Pearl 

 (1907). In a certain Culture IV., I found conjugants varying in 

 dimensions from 148 X 44 to 260 X 60 microns. I have found (not 

 in the same culture) conjugants with length as low as 100 microns. 

 It is clear, therefore, that not all individuals are of the same size 

 at conjugation. There is no reason to expect them to be so, there- 

 fore, at other definite periods in the life cycle; as we have seen, they 

 are not. Selection of small pairs gives small progeny ; of large pairs, 

 large progeny. 



2. In certain of my pure lines whose history was followed for a 

 long time and whose dimxcnsions were taken at intervals, conjugation 

 occurred at times, but the dimensions at such times were not very 

 dift"erent from the dimensions at other periods in the life history. 

 Thus, in the earlier sections of this paper we have dealt witn two 

 pure lines, D and c ; the former showed usually a mean length of 

 about 180 microns, the latter a mean length of about 130 microns 

 (see Table XVIII. ). At a certain time an epidemic of conjugation 

 arose in c. The mean dimensions were indeed higher than usual 

 at that time, the mean length of the conjugants rising to 158.496 

 microns. But this does not by any means bring it up to the ordinary 

 mean of D, and immediately after conjugation (in five days) the 

 mean length of c fell back to 129.640 microns. Again, in the small 

 race g, of Table XXIII. , conjugation occurred in a number of cases ; 

 a typical pair measured but no microns in length. In other lines I 

 have found for the conjugants means as high as 199.024 and as low 



