CONJUGATION AND ENCYSTMENT 349 



alternating; for an organism that can produce 1646 vegetative 

 generations can in all probability continue reproducing asexu- 

 ally indefinitely. There is, in fact, no evidence of cycles any- 

 where in the entire experiment. Toward th6 close there was to 

 be sure a loss in vigor, but the loss was quite as great in the 

 group of lines which had produced only 850 generations as it 

 was in the one which had produced 1559 generations. 



But if conjugation and encystment do not cause an increase in 

 the rate of fission, how can the follomng results obtained by 

 Calkins be explained? And if conjugation is not a rejuvenating 

 process, what is its function? 



Calkins in 1904 cultivated on slides a line of paramecia for 

 369 generations; then he started a new line from some of the in- 

 dividuals of this line, after they had conjugated, and carried it 

 along parallel with the old line for nine months. During this 

 time the former (ex-conjugant) produced 396 generations and 

 the latter (non-con jugant) only 277 (Calkins and Gregory, '13, 

 p. 517). 



These results seem strongly to support Calkins' conclusion 

 that conjugation causes an increase in the vitality of protozoa. 

 The support is, however, not so strong as it seems. In the first 

 place, both lines were not treated identically. ''The ex-conju- 

 gant was treated for twenty-four hours with beef extract on De- 

 cember 9th, the A series (non-con jugant) with beef extract on 

 December 14th, January 8th and 15th." It is not possible to 

 say what effect this different treatment may have had, and it 

 is, therefore, evident that it may have caused the observed 

 difference in rate of fission. In the second place. Calkins and 

 Gregory maintain that in different lines originating in the same 

 individual there is a marked difference in the rate of fission. 

 They say ('13, p. 477) concerning four such lines. A, B, C and 

 D "In one hundred days a typical representation of A would 

 have divided 65 times, of B, 90 times, of C, 81 times and of 

 D, 95 times." Accordingly, if D had produced 396 generations, 

 the number produced by Calkins' ex-conjugants mentioned 

 above, A would have produced only 270.9 generations, that is, 

 six generations less than Calkins' non-conjugants. It is con- 



