352 



THE AMEBIC 



'RALIsr [Vol. LI 



168, 166, and 168. Thus it is obvious that in the ancestors 

 of the mutants nothing in the nature of mutations in the 

 rate of fission had occurred for many generations. This 

 indicates that mutations do not ordinarily occur in asexual 

 reproduction. 



During the period of 40 days mentioned above, ending 

 July 10, all of the lines were in excellent condition and 

 not a single individual died. On July 12, however, one 

 line died out and on the 14th three more died, leaving but 

 one line. For several days preceding the temperature 

 was very high. It was recorded twice daily and these 

 records show that it reached a maximum on July 9, when 

 it was 28.5^ at 7 : 30 a.m. and 31° at 6 p.m. It was, how- 

 ever, high continuously from the 4th on, and during this 

 period reproduction was exceedingly rapid, as Table I 

 indicates. It was at the close of this period of rapid mul- 

 tiplication that the four lines mentioned above died out 

 and it is probable that this extraordinary environmental 

 condition had much to do with the nature of the variations 

 in the progeny of the remaining line, although similar 

 variations did not occur in four other groups of lines that 

 wtTc rniining pai-allel with the one under consideration. 



From tile roiiiaiiiing line mentioned above five new lines 

 were start^Ml on July 1"). For the first five days, the rate 

 of fi->ioii in tlie-c liiK's was nearly the same, the total 

 nninlici- per liti.' 1h in-- 2(;. 27, 28, 26 and 28, respectively. 

 During- tlie uoxt live days tlie difference became somewhat 

 greater, the total number of fissions per line being 21, 19, 

 18. 17 and 17. re>])ectively. On the day following this 

 period, the line which had produced 19 fissions died out 

 and was replaced by a new line from the one which had 

 produced 21. There were thus two lines having more 

 rapidly, and three lines having less rapidly, dividing an- 

 cestors, all, however, originating from the same indi- 

 vidual. On October 14 the lines in both groups were in- 

 creased to fi\e and thus they were continued until the 

 close of the experiment, which extended through 315 days. 

 The individuals in all of the lines in each group repro- 



