444 JENNINGS— HEREDITY IN PROTOZOA. [April 24, 



mens in which constriction is beginning. Among the 313 dividing 

 specimens of lot i (Table XI.) there were 131 in which the depth 

 of the constriction below the body surface was less than one unit 

 of the micrometer scale (less than 4 microns). These may be taken 

 as representing the earliest stages of fission. The depth of the con- 

 striction is in these specimens less than one twelfth the breadth. 

 Their measurements are given in Table XIII., while the constants 

 deduced from the measurements are shown in row 25, Table X. 

 These should be compared with the measurements and constants for 

 the random sample of the specimens not dividing in this same culture 

 (Table XIV., and row 27, Table X.). 



Examination of these tables shows the following remarkable facts : 



1. The mean length of the specimens beginning fission (175.696 

 microns) is much less than the mean length of the random sample 

 (199.960 microns) — although the latter must contain many specimens 

 that have not reached adult size. 



2. The range of variation in length is much less in the specimens 

 beginning fission than in the culture as a whole. In those beginning 

 division the range is from 156 to 204 microns; in the random sample 

 it is from 148 to 240 microns. 



3. The longest specimens beginning fission are 36 microns shorter 

 than the longest of the random sample. In the random sample, 34.5 

 per cent, of all the specimens are longer than the longest of those 

 beginning fission, while 95.5 per cent, are longer than the mean length 

 of the specimens beginning fission. 



4. The variation in length is decidedly less in the specimens 

 beginning fission than in the random sample. In the lot beginning 

 fission the coefficient of variation is but 5.368, while in the random 

 sample it is 7.636. 



It may here be noticed that coefficient of variation in the speci- 

 mens beginning fission is less than that for conjugating specimens, as 

 studied by Pearl (1907). To this matter we shall return later. 



5. In the specimens beginning fission the mean breadth (55.480 

 microns) is greater than the mean breadth of the random sample 

 (50.220 microns). 



6. The variation in lireadth is nnich less in the specimens begin- 



