Internal Characteristics and Size 113 



jugation rather than due to those circumstances very- 

 unfavorable to growth by which conjugation is usually 

 induced. The most representative observations were 

 made by Maupas ('89), who noted that under starva- 

 tion conditions several successive fissions were likely to 

 occur, without intervening growth, as a preamble to 

 conjugation. Such he believed to be the case in the 

 ciliates Didinium, Enchelys, Leucophrys, and Vorti- 

 cella. Of course, growth was impossible without food ; 

 and Maupas did not record the actual number of gen- 

 erations which did not grow, nor insure that the star- 

 vation was absolute. 



After conjugation. Just after conjugation fission 

 has been observed to proceed at slow rates for several 

 generations. Joukowsky ('98) noted this to be the 

 case in Stylonychia, Jennings ('08b) in Paramecium, 

 and Calkins ('19) in Uroleptus. During such a period 

 the individuals were observed to be unusually large. 

 But after a few generations, in Jennings's cultures, the 

 dimensions were the same as they subsequently were in 

 their descendants which flourished several months 

 later. In these few generations which were unusually 

 large, the readjustment of the nuclear conditions by 

 the formation of new macronuclei occurred, and slow 

 fission as well as large size accompanied this process. 

 Other observers failed to find any deviation of fission 

 rate after conjugation, particularly in Paramecium 

 (Simpson, '01) ; evidently conditions need to be highly 

 controlled in order to evaluate it. In later generations 

 conjugation is recognized to lead to increased rates 

 of reproduction in a number of species, particularly in 

 Uroleptus (Calkins, '19), Spathidium (Woodruff, '25), 

 and Blepharisma (Woodruff, '28). 



Calkins and Gregory ('13) followed further the in- 

 fluence of conjugation in Paramecium upon the sizes of 

 the descendants. They cultivated separately lines 



