372 H. S. JENNINGS 



results given in the present paper, where the reverse is shown to 

 be the rule, it is clear that these observations of Maupas do not 

 touch the matter at all. 



One single case only Maupas has which makes even an approach 

 to the form of this necessary demonstration, and this, as we shall 

 see, really gives no evidence at all. This is the case of one of his 

 cultures of Stylonychia pustulata ('88, pp. 196-201). A line of 

 propagation was begun with a single individual, November 1, 

 1885. This hne died out on March 26, 1886, after 215 genera- 

 tions. On February 22 a single specimen of the 156th generation 

 was taken from this line and allowed to conjugate with an indi- 

 vidual from outside. Maupas tells us on page 323 of his paper 

 of '89 that these individuals from outside, which he mixed with 

 those from the long-continued cultures ''were taken at hazard 

 in my small aquaria." Thus such an individual had not been 

 living under the peculiar conditions of these experiments. De- 

 rived from this pair a new line of propagation was continued 

 for 316 generations (till July 10, 1886), while the old hne from 

 which one of these ex-conjugants came, died out after but 59 

 generations more. 



Now, the work of Enriques, Woodruff, Baitsell ('12), et cetera, 

 has shown that the conditions with which Maupas worked result 

 after a time in depression of the vital functions, but that animals 

 kept under more- favorable conditions do not show such depres- 

 sion, even though they have lived as long without conjugation 

 as the depressed race. The depression is due to the conditions, 

 not to lack of conjugation. What Maupas did was to take from 

 outside a fresh, vigorous specimen, and mate it with one of these 

 depressed ones. He then found that the progeny were vigorous. 

 He does not note whether the line of progeny he used came from the 

 depressed mernber of the pair, or from the vigorous one, although 

 this is an absolutely essential point for determining whether the 

 depressed stock was rejuvenated even by conjugation with a 

 vigorous one. The probability is strong that the new line of 

 propagation came from the new, vigorous individual. But such 

 an individual would have given an equally long series of vegeta- 

 tive propagations if it had not been mated at the beginning. Its 



