CONDITIONS FOR CONJUGATION 343 



It is apparent from these statements that Zweibaum holds 

 that the conditions for conjugation as worked out for one race 

 of Paramecium apply to all other races of the same species — at 

 least in P. caudatum; and he strongly inclines toward the view 

 that conjugation is regulated primarily through environmental 

 conditions. This, at any rate, is the view expressed by Enriques 

 (on the basis of Zweibaum's work^), for he did not see fit to change 

 his original point of view, believing that the preliminary period 

 of semistarvation of five to six weeks to which the paramecia 

 were subjected was but a step in the experimental procedure, 

 making the organisms more susceptible to the effects of the 

 salts. 



The present study was undertaken mainly with this object 

 in view: to ascertain whether the so-called 'conditions for 

 conjugation' worked out for one race of Paramecium are effective 

 for other races and, in general, to determine so far as possible 

 the differences in the conditions required to induce conjugation 

 in different races. An attempt was made, also, to find out 

 whether the various races under observation were characterized 

 by different time intervals between conjugation periods, or, as 

 we might say, by diverse 'sexual periodicities.' Jennings ('10) 

 called attention to such apparent periodicities in certain races 

 of P. aurelia. His studies on P. caudatum, while less extensive, 

 indicated that in some races of this species conjugation occurs 

 at intervals of several months, or perhaps years. The impor- 

 tance of further work relative to this point was felt more keenly 

 in view of the greater perfection attained in the experimental 

 (or environmental) study of conjugation. Even in other groups 

 of organisms the study of natural periodicities in respect to 

 sexual activity, apart from environmental influences, has not 

 received the attention which it merits. 



This work was undertaken at Dr. H. S. Jennings' suggestion, 

 with this end in view. I wish here to express my thanks to 

 Professor Jennings for his kindly advice and criticism, as well 

 as for assistance in the procuring and rearing of material for 

 cultures. 



1 See Zweibaum ('12), footnote by Enriques, pp. 346-347. 



THE JOURNAI, OF EXPERIMENTAL ZOOLOGY, VOL. 34, NO. 3 



