154 GARY N. CALKINS 



This is the same optimum as that following conjugation. The 

 M series is pedigreed. It came from the F series in its 45th 

 generation, and after a period of six and a half months was re- 

 covered fron the cyst. During the sixty days subsequent to the 

 date of the 45th generation, the F series divided at the rate of 

 17.6 times in ten days, while the protoplasm of the M series 

 during its first sixty days of culture divided at the rate of 19.8 

 times in ten days. The difference (2,2 divisions) is undoubtedly 

 greater than it would have been had the temperature conditions 

 remained the same. As explained on page 151, the M series was 

 cultivated under conditions of higher temperature than the 

 laboratory, whereas the F series was cultivated under the lab- 

 oratory temperature. The L series, which came from the F 

 series through conjugations and which was started at approxi- 

 mately the same time as the M series, was cultivated under the 

 same conditions as the M series. Its division rate during this 

 same period of sixty days was 18.8 — one full division higher than 

 the usual ex-conjugant. In this case of the M series, therefore, 

 the rejuvenating effect of parthenogenesis was even greater than 

 that of conjugation. Whether the endurance of the partheno- 

 genetic protoplasm differs from that of the protoplasm following 

 conjugation remains to be seen. 



Parthenogenesis through encystment appears to be an attribute 

 of high vitality, and the ability to encyst is apparently lost at an 

 early date (diagram 1). In the C series it did not occur after 

 the 160th day; in the F series, not after the 110th day, and in 

 the D, I, and J series it did not occur after the 80th, 60th and 

 20th days, respectively. I do not know what this means, but 

 it is certainly true that no internal reorganization without en- 

 cystment has occurred thus far, for in every series the physio- 

 logical depression is continuous and progressive, and death in- 

 variably follows. Conjugation, with rejuvenescence, however, is 

 possible almost to the end of the cycle. Encystment, apparently, 

 is not possible near the end of the cycle, but it does occur even 

 in the first ten days after conjugation. Conjugation, on the 

 other hand, does not occur until from thirty to seventy days 

 after the previous conjugation. I am aware of published state- 



