504 J. A. DAWSON 



The production of an amicronucleate race of Paramecium has 

 been claimed by Lewin ('10), who obtained, by cutting, an 

 amicronucleate fragment which regenerated and produced the 

 'amicronucleate race.' This race reproduced by fission for 

 nearly two months and was normal in every respect except for 

 the absence of a micronucleus. It is also interesting to note 

 that LeDantec ('97) stated that, in the case of a ciliate (un- 

 named, with an elongated macronucleus and a single micro- 

 nucleus, a merozoite containing a portion of the macronucleus 

 only regenerated a micronucleus. The results of both these 

 investigators were published in short preliminary papers and, 

 pending more substantial proof or confirmation by other workers, 

 must be regarded as interesting possibilities rather than as 

 established facts. 



The form described in this paper differs from all previously 

 described hypotrichous ciliates in that it has never at any 

 stage in its life-history, since it has been under observation, 

 contained a definitive micronucleus. This statement is made as 

 a result of long-continued and careful cytological study of many 

 preparations of this form throughout the various stages of its 

 life-history during a period of over two years. 



As already stated, in other groups than the hypotrichs in 

 which no micronucleus is visible during the vegetative stages it 

 was invariably, during sexual phases of the life-history, found 

 to be present in more or less close connection with the macro- 

 nucleus, so that the usual dimorphic nucleus was represented 

 apparently during the vegetative condition by a macronucleus 

 alone, i.e., the macronucleus thus was an amphinucleus contain- 

 ing both tropho- and idiochromatin. In this form, therefore, 

 since obvious but abortive attempts to conjugate occurred fre- 

 quently, there is ground for considering that the nucleus is an 

 amphinucleus, representing both the tropho- and idiochromatic 

 phases. 



It is believed by the recent investigators (Woodruff, '05, '13; 

 Baitsell, '14) who have done extensive experimental work on 

 the life-history of the hypotrichida, that these forms will live 

 indefinitely without conjugation or artificial stimulation, pro- 



