140 GARY N. CALKINS 



only 13.4 divisions in its first ten-day period, was considerably 

 lower than that of the parent C series, which was 15.6 for the 

 same calendar period. These fluctuations disappear by using 

 the longer, sixty-day period, where in every case the mean di- 

 vision rate of the filial series is greater than that of the parental 

 series for the same period (table 5) . 



The mean division rates for the second sixty-day periods show 

 a decreased vitality in every series (table 4). Here, again, there 

 is a remarkable uniformity of results, although variations are more 

 marked than in the first sixty-day period. The decrease in the 

 vitality of the H series in this second period is so slight that it 

 would not be noticed were it not for the decrease in all series — 

 a decrease which is especially noticeable in the F and J series. 



In the third sixty-day period there is a similar decrease in 

 vitality over the second sixty-day period in all series, and the 

 variations in different series become still greater. Compared 

 with the second sixty-day period, the decrease in vitality is again 

 slight, but compared with the first sixty-day periods, the decrease 

 in vitality becomes sufficiently large to indicate an indisputable 

 waning of vitality in all series. 



In the fourth sixty-day periods the vitality shows a marked 

 drop in all series that have passed through this age, and here the 

 variations in different series are extreme. The D series, for 

 example, drops from an average of eleven and a half divisions to 

 seven-tenths of one division in ten days. On the other hand, 

 the F series dropped only from twelve and six-tenths to nine and 

 seven-tenths divisions in ten days. 



The precipitous fall in vitality manifested during this fourth 

 period of sixty days is continued into the fifth period. Only a 

 few of the series outlive this sixty-day period, indeed, only the 

 protoplasm of the C series was alive at the end of three hundred 

 days, that of the A series dying during the last week of this fifth 

 period. The decline in vigor and early death were most marked 

 in the F and H series, the former dying four weeks, the latter, 

 three days after the end of the fourth period, 



Maupas found that the last individuals of a race were deformed, 

 reduced in size, and degenerate through loss of micronuclei and 



