EFFECT OF CONJUGATION • 281 



sents. The fundamental experiment is to divide a given stock 

 into two parts, kept under identical conditions, permitting one 

 part to conjugate and preventing the other; to keep these further 

 under identical conditions, and to determine in what respects 

 they differ. In the few attempts that have heretofore been made 

 to observe directly the results of conjugation, the control series 

 (of the same stock without conjugation) has almost invariably 

 been omitted, so that it is uncertain how far the phenomena 

 observed v/ould have occurred equally if there had been no 

 conjugation.- 



In the investigation here set forth this fundamental experiment 

 has been many times repeated, with careful study of the various 

 characteristics of the set that have conjugated, as compared with 

 those of the set that have not conjugated. Besides an account 

 of the results of this fundamental experiment, the paper deals 

 with certain other problems connected with the physiology of 

 conjugation. The effect of conjugation on the size of the indi- 

 viduals of the stock has been set forth in a former paper (Jennings 



'11). 



Thus the matters dealt with in the present paper are mainly 

 the following: the effects of conjugation on the rate of multi- 

 plication; on survival and mortality; on the general vigor; its 

 relation to 'rejuvenescence;' the effects of conjugation among 

 close relatives; the effects of continued inbreeding; the results of 

 allowing a stock to conjugate many times in a given period, as 

 compared with causing it to multiply without conjugation for 

 the same period; the relation of conjugation to inheritance, and 

 the effect of conjugation on variation. 



Each experiment gives evidence on most of the matters just 

 mentioned, so that it is not possible to separate fully the dif- 

 ferent subjects. The experimental results will first be presented 

 systematically, with more particular reference to the effects of 

 conjugation on vigor, multiplication, survival and variation, then 

 each of the topics will be taken up, and an analysis given of the 

 experimental evidence bearing upon it. 



- The only exception to this that I have found is in the experiment of R. Hert- 

 wip;, briefly set forth in his paper of 1889; this will be taken up later. 



