x9o8.] JENNINGS— HEREDITY IN PROTOZOA. 433 



various ages and measurements are given, with those of a random 

 sample of the culture in lot 6, Table X. 



The first set taken consisted of but 24 specimens, aged from o 

 to 19 minutes. Though the number is small it is worth while to 

 work out the constants for comparison with other stages in this same 

 culture ; it must be remembered that it is extremely difficult to get 

 large numbers at any one time of individuals so young. The meas- 

 urements are given in Table XXXI., while the constants are shown 

 in row 7, Table X. For comparison with these a second lot of the 

 same age, but containing 39 specimens, was taken from the same 

 culture two weeks later. The measurements are given in Table 

 XXXII. ; the constants in row 13, Table X. The constants for the 

 two sets taken together (63 specimens aged o to 19 minutes) are 

 given in row 14, Table X. 



Comparing these with the specimens but o to 5 minutes old, we 

 find that the mean length has increased by 36 to 40 microns. The 

 breadth is about the same in one of the lots (row 13, Table X.), but 

 is much greater in the other (row 7). This difference is due to 

 environmental effects. The coefficient of variability in length shows 

 a decided decrease, indicating that growth is relatively more rapid 

 during the first five minutes than later. The correlation between 

 length and breadth is, as might be expected, negative in the sets o to 

 19 minutes old, as it was in the set still younger. 



A number of specimens were killed at precisely known ages, and 

 the measurements taken. Thus, from lot 7 (row 13, Table X.) a 

 typical pair of young at the moment of separation measured no X 52 

 microns. At the age of one minute the two members of a pair 

 measured each 124 X 52 microns ; at two minutes another pair were 

 each 120 X 52 microns. At three minutes one member of a pair 

 measured 120 X 48 microns, the other 124 X 44- At five minutes 

 the lengths of the two resulting from a certain fission were respect- 

 ively 124 X 48 and 112 X 44 microns. Five specimens kept till they 

 were precisely nineteen minutes old measured respectively 160 X 48 

 microns; 160X44; 152X36; 152X40; 156X44. The mean di- 

 mensions were thus 156 X 42.4 microns. 



Outlines of individuals from o to 19 minutes old, showing the 



