486 JENNINGS— HEREDITY IN PROTOZOA. [April 24, 



individuals corresponding in many respects to the c line, with a 

 mean size on November 14, 1907, of 140.133 microns. These two 

 sets occurred mixed, but each reached its maximum development at 

 the dates mentioned. Isolated samples of the two sets retained their 

 characteristic differences in size, just as happened in the case of 

 D and c. 



But the interesting condition showed itself in the smaller set. 

 An-ong these were individuals of such different cizes, that in spite 

 of our knowledge of the great differences produced by growth and 

 environment, it seemed worth while to try to isolate and breed them. 

 In a random sample of 60 specimens the length varied from 96 to 

 176 microns — the smaller sizes being grouped about 120 microns, the 

 larger about 160 microns. 



Accordingly, on November 9, 1907, I separated two lots, one 

 containing ten of the smaller specimens, the other ten of the larger 

 ones. These were placed in watch-glasses with equal quantities of 

 the same culture fluid, and kept under identical conditions, where 

 they were allowed to multiply. One week later (November 16) 

 thirty specimens measured from each showed mean dimensions of 

 125.600 X 36.200 microns for the progeny of the larger ten, 96.400 

 X 30.00 microns for the progeny of the smaller ten. On November 

 27, a random sample of 100 from each gave for the progeny of the 

 larger ten, dimensions of 134.320 X 36.280 microns; for the smaller 

 set, 92.240 X 26.920 microns. Thirty-seven days later (January 2, 

 1908) the two lots still showed their characteristic differences, though 

 cultivated under identical conditions. The mean dimensions of the 

 two sets (from random samples of 100) were now 134.360 X 33-440 

 microns (for the larger), and 104.208X26.583 microns (for the 

 smaller). 



Thus, we have clearly two sets, with differences in size persisting 

 from generation to generation (in spite of fluctuations in each due 

 to environmental changes), and both falling, in a general way, in the 

 dimensions previously found for the line c. It is evident, therefore, 

 that D and c did not represent the only existing different lines. 



Since the two sets under experimentation had come each from 

 ten individuals which may be of heterogeneous origin, I isolated 

 from each, as soon as it was evident tliat thev were retaining their 



