370 H. S. JENNINGS 



sort of regenerating ferment, restoring all its vital energies, et 

 cetera. 



The grounds for this view have consisted, almost exclusively, 

 not in actual observation of any such rejuvenizing action by con- 

 jugation, but in the observation that during vegetative repro- 

 duction under experimental conditions the organisms become 

 depressed, degenerate, and finally die. From this it was con- 

 cluded that conjugation must be what remedies this. 



This line of argument has, however, quite lost its force, in view 

 of the modern work of Calkins, Enriques, Woodruff, and others. 

 These authors' results demonstrate that the very limited periods 

 within which Maupas observed degeneration has no significance 

 for the question as to whether degeneration is an inevitable 

 consequence of continued reproduction without conjugation, for 

 they kept vegetative reproduction in progress for periods many 

 times as long as those which Maupas found to result in degenera- 

 tion. The work of Woodruff, in particular, seems to show that 

 Paramecium may be kept multiplying vegetatively for an indefi- 

 nite period. Furthermore, the work of Enriques and of Woodruff 

 has shown to what the degeneration observed by Maupas was 

 due. Under proper nutritive and chemical conditions no such 

 degeneration appears. 



It is not necessary to review in detail this vast subject, but 

 ther^ will hardly be any dissent from the statement that the 

 modern work has largely, if not entirely, deprived of its force this 

 argument for the necessity of conjugation. 



All the more therefore we are driven to examine the direct 

 evidence as to the rejuvenating effect of conjugation. And in 

 doing so, we must reflect that if the argument above mentioned 

 were valid, there should be no difficulty in observing experimen- 

 tally the rejuvenating effect; so that a fortiori we must demand 

 what this direct evidence is. 



In reading Maupas' great works ('88, '89) in search of this 

 direct evidence for a rejuvenating effect of conjugation, one is 

 astonished at the way it eludes one at every step. Most of the 

 actual observations that bear on the matter at all, seem indeed 



