CONJUGATION AND ENCYSTMENT IN DIDINIUM 



NASUTUM WITH ESPECIAL REFERENCE TO 



THEIR SIGNIFICANCE 



S. O. MAST 

 From the Zoological Lohoratory of the Johns Hopkins University 



CONTENTS 



Introduction 335 



Material and methods 338 



Nature and cause of encystment, vitality and activation of cysts 340 



Nature, cause and duration of conjugation 341 



The effect of conjugation and encystment on the rate of fission 343 



The effect of conjugation on death-rate 354 



The effect of conjugation on variation in the rate of fission 356 



Summary 357 



Literature cited 359 



INTRODUCTION 



That conjugation is a rejuvenating proceSvS of some sort or 

 another has been very widely held. Engelmann ('76), Biitschli 

 (76), Maupas ('88 and '89), Hertmg ('89), Calkins ('06, '09, 

 '13) and many others support this idea. Not all of these inves- 

 tigators agree with reference to the details concerning the 

 rejuvenating effect, but i)ractically all hold that if conjugation 

 is prevented the race dies out, indicating that the progeny of a 

 single individual passes through periods of vitality correspond- 

 ing somewhat to youth, maturity and old age in metazoon 

 individuals. 



Calkins has very ably championed this view. He says ('09, 

 p. 103) referring to the offspring of an exconjugant: 



If at any given period [we] could combine them in one mass of 

 cells, we should have the analogue of a metazoon and would find that 

 the protoplasm represented by the aggregate cells would manifest the 

 same successive periods of vitality as those of youth, adolescence, and 

 old age in Metazoa. We would find that the young cells divided more 



335 



