DIDINIUM NASUTUM 



I, THE LIFE HISTORY 



GARY N. CALKINS 

 From the Department of Zoology, Columbia University 



TWELVE FIGURES — ONE PLATE 



The work of Woodruff and Erdmann ('14) on Paramecium 

 aurelia showing the occurrence of periodic reorganization of the 

 cell, which, like conjugation, has the effect of renewing vitality, 

 raises the question as to the length of life of a ciliated protozoon 

 and its progeny in which both asexual reorganization and conju- 

 gation are prevented. Fermor ('13) has shown that a similar 

 reorganization occurs in Stylonichia during the process of encyst- 

 ment, Prandtl ('06) made the statement, unsupported by evi- 

 dence, however, that in Didinium nasutum nuclear reduction 

 occurs during encystment as well as during conjugation. These 

 observations indicate that encystment in ciliates, when not for 

 purposes of protection against adverse environmental conditions 

 or for division (as in Tillina), is a process during which nuclear 

 reorganization, or parthenogenesis, takes place. An encysting 

 organism in which asexual endomixis takes place has advantages 

 over Paramecium in the present problem because of the defiAite 

 external advertisement of the internal processes taking place. 



Didinium nasutum was chosen for the experiments because of 

 its large size, its easily controlled feeding habits and because of 

 its readiness to encyst. The feeding habits have been worked 

 out by Mast ('09) and the process of conjugation by Prandtl ('06) . 



MATERIAL AND METHOD 



Two individuals — X and Y — of Didinium nasutum were iso- 

 lated from fresh material brought into the laboratory from 

 Van Cortlandt lake on October 28th, 1914. They were placed 

 in ground-glass flat-bottomed culture dishes each containing 0.25 



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