566 THE POPULAR SCIENCE MONTHLY 



tions raised above all doubt.^ Yet tbis statement, though it seemed to 

 rest on irrefragable evidence, and agreed with everything else that was 

 known, was quite false, and in Maupas's time had been completely 

 abandoned. Perhaps this was a type of the fate to be met by many 

 other supposed demonstrations as to the function of conjugation, in- 

 cluding that of Maupas — and not impossibly the one here presented. 



Before leaving the work of Maupas, we must mention certain other 

 observations that he made which are of great importance for under- 

 standing the matter. In his experiments, after degeneration had be- 

 gun, many specimens within the same series (all derived from the same 

 parent) conjugated together. But this did not rejuvenate them. On 

 the contrary they died all the sooner after conjugating with close rela- 

 tives. This happened in many cases. 



So Maupas concluded (1) that conjugation with close relatives does 

 not rejuvenate; (2) that conjugation with related individuals is not 

 merely useless, but destructive; as soon as they do this, says Maupas, 

 their doom is sealed; (3) that rejuvenation is due to conjugation with 

 unrelated individuals. 



This work of Maupas had of course tremendous influence ; it seemed 

 to be definitive. There appeared to be no escape from his conclusions, 

 and for many years they were hardly seriously questioned. 



But in very recent times have come a series of investigations that 

 have shaken the conclusions of Maupas and given the entire matter a 

 new aspect. It appears to me that the time is ripe for a revision of 

 judgment on the whole general problem of age, death and conjugation 

 in these lower organisms. I shall attempt to give briefly the grounds 

 for such a revision, and the direction which the final judgment must 

 apparently take. 



1. The credit for seriously opening the question anew, as well as 

 for getting some of the most important evidence leading to what seem 

 to me the correct conclusions, is due to Calkins in his investigations ex- 

 tending from 1901 to 1904. After cultivating Paramecium for about 

 200 generations (three months) without conjugation, Calkins found 

 that they become depressed; the division rate decreases; many die. As 

 you remember, he found that by changing the diet at these periods, by 

 transferring from hay infusion to beef extract, to pancreas or brain ex- 

 tract — the animals could be revived, and their life and propagation 

 continued. In this way he kept them for 742 generations (23 months), 

 but at the end of that period they finally died, in spite of any changes 

 that were made in their food. This showed that the infusoria could be 

 kept alive without conjugation a much longer time than Maupas had 

 observed. Calkins kept his animals for more than twice as many gen- 

 erations as did Maupas. 



= See Engelmann, Zeitschr. f. wiss. Zool, II. (1862), p. 347. 



