ADTHOR S ABSTRACT OF THIS PAPER ISSUED 

 BY THE BIBLIOGRAPHIC SERVICE, AUGUST 11 



UROLEPTUS MOBILIS ENGELM. 



II. RENEWAL OF VITALITY THROUGH CONJUGATION 



GARY N. CALKINS 

 Columbia University, New York City. 



ONE CHART AND ONE FIGURE 



In a previous paper I have described the morphology and the 

 cytology of division and conjugation stages of the rare hypo- 

 trichous ciliate which forms the subject of the present paper. ^ 

 Lending itself admirably to the cultural method which has been 

 employed, Uroleptus mobilis is the most satisfactory organism 

 for experimental work I have yet encountered. Paedogamous 

 conjugation, in epidemic form, occurs readily, under the proper 

 conditions, in the culture medium. Ex-con jugants, upon iso- 

 lation, live and thrive in this culture medium in practically 100 

 per cent of cases — a rare phenomenon among the hypotrichs. 

 Asexual reorganization, or parthenogenesis, called by Woodruff 

 and Erdmann 'endomixis', occurs at fairly definite periods, un- 

 der the protection of a cyst membrane. Such reorganizations, 

 therefore, are advertised by the form assumed by the organisms 

 and do not interfere with the study of comparative vitality 

 throughout the life cycle. 



Starting with a single individual which was isolated imme- 

 diately after conjugation, on November 16, 1917, I have followed 

 the life history of thirteen different series, all beginning as ex- 

 conjugants of pairs of normally conjugating individuals, and all 

 were progeny of the original ex-con jugant which was isolated 

 November 16, 1917. Three additional series, derived from 

 encysted individuals, have also been studied in similar isolation 

 cultures. The different series were started at various periods 



1 Calkins, 1919. Uroleptus mobilis, Engelm. I. History of the nuclei during 

 Division and Conjugation. Jour. Exp. Zool., vol. 27, no. 3, p. 293. 



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