438 JENNINGS— HEREDITY IN PROTOZOA. [April 24, 



nets of a second division ; either one of the twelve-hour specimens 

 had divided, or there was accidentally taken with them an older 

 specimen which divided. In either case these two specimens do not 

 belong in the twelve-hour lot, as they are much younger. On this 

 account I have calculated the constants for this twelve-hour lot twice, 

 once including these two small specimens (row 20, Table X.), the 

 second time excluding them (row 21). The variability in length is 

 much reduced — from 6.672 to 4.930 — by the omission of these two. 

 At the same time the correlation between length and breadth is like- 

 wise reduced from .4868 to .3474. 



(i) Age 18 Hours {Table XL., and rozv 22, Table X.). — Growth 

 in length continues, though very slowly ; in six hours the increase 

 has been less than during the first five minutes after separation. The 

 anim.als at this age are decidedly longer than the mean for the cul- 

 ture as a whole, as judged from the random sample of Table VII. 

 (page — ), taken three days earlier. The mean breadth of the 

 eighteen-hour specimens, while greater than that of the random 

 sample, has decreased as compared with that of those only twelve 

 hours old. 



The variability of these two lots (12 and 18 hours old) of adult 

 size is less than that of the random samples (for examples, rows 3, 

 6, 12, 19, Table X.). 



Fifth Stage: 24 Hours Old {Table XLL, and row 2^, Table X.). 

 A final lot of 300 specimens was selected while dividing and 

 these were kept till they were 24 hours old. These were progeny 

 of D, but were taken from the culture somewhat more than a month 

 later than those o to 18 hours old. To understand their measure- 

 ments it is necessary to take into consideration the cultural condi- 

 tions. These animals were living in an ordinary hay culture, which 

 was getting old, so that they were not dividing rapidly; they were 

 rather slender in form. Now a large number of these was placed 

 in a fresh decoction of hay and left there for 24 hours. They 

 increased in size and began to divide rapidly. Now 150 dividing 

 specimens (producing, of course, 300 young) were taken out and 

 returned to the original culture fluid. This was for the purpose of 

 preventing a second division before the end of the period of twenty- 



