298 GARY N. CALKINS 
divided, on the average, thirteen times in ten days throughout 
the entire life-cycle, and seventeen times in ten days during its 
period of youth. Its metabolic activities, therefore, were high, 
but it also lacked in endurance, living only 210 days. Its off- 
spring, the P series, had the same virility in metabolic activity, 
but it was combined with endurance which gave the P series its 
high relative vitality of 95 per cent. It is quite probable, there- 
fore, that the relatively low vitality of the L series was due to 
other causes than age of the parents at the time of conjugation. 
Returning once more to the extremely weak series, it remains 
to be seen whether their weakness was due to congenital causes 
or to environmental influences. It must be emphasized, however, 
that environmental conditions have been maintained as nearly 
as possible the same for all series, and exactly the same for series 
under culture at the same time, so too much stress must not 
be placed on the factor of environment. ‘The Q series, for ex- 
ample, had an average division rate of only 6.6 divisions per 
ten days of its thirty-five days of life, while its initial division 
rate was only 6.7 and its amount of rejuvenescence only 5.2 
(ef. table 3). Its parent, the I series continued to live after the 
@ series had died, even though it was 316 generations old when 
the Q series was started. The I series was thus extremely old 
at this time and had the characteristic weakness of old age, yet 
it showed no effect of possible adverse environmental factors 
which might have been responsible for the weakness and early 
death of its progeny, the Q series. Furthermore, the Q series 
divided for the first time on January 23, 1919, and the P series 
divided for the first time on January 15th. The two series thus 
were carried on at the same time and were subject to the same 
’ environmental influences, yet the Q series divided in all only 
23 times while the P series divided 327 times. The weakness 
of the Q series cannot be attributed to adverse environmental 
causes. 
The protoplasm of the a series also was consistently weak 
throughout. Its division rate for the entire life-cycle was 10.7 
divisions per ten-day periods and only 13.2 divisions during its 
period of youth. It divided only 159 times in 148 days and its 
