REGENERATION OF PLEUROTRICHA. 175 



that which Calkins 2 has found to exist between the so-called 

 Paramecium caudatum and Paramecium aurelia, except that there 

 it is a variation in the number of micronuclei; here, a variation 

 in the number of macronuclei. It appears possible that by 

 proper selection a strain of Pleurotricha may be obtained in 

 which all of the animals, for a period, may show only one macro- 

 nucleus. 



From the experiments it appears fairly conclusive that mero- 

 tomy generally has no effect on the normal number of micro- 

 nuclei. Animals with less macronuclei than the normal may be 

 found both in laboratory cultures of this animal and among the 

 descendants of merozoa. Animals with more than the normal 

 number of micronuclei may occur in laboratory cultures. The 

 single instance in which there was found among the merozoa an 

 animal with two abnormal macronuclei and several micronuclei 

 is undoubtedly that of a degenerative or a necrobiotic cell. This 

 is somewhat suggestive that multiple micronuclei may in general 

 be one of the manifestations of a degenerative or a necrobiotic 

 process in the cell. 



It is to be noted that these observations are not in accord with 

 Lewin's findings for Stylonychia. It appears from his paper that 

 he had some difficulty in getting his animals to survive in the 

 media used and another possible explanation for his observations 

 is that they were more the results of necrobiosis and degeneration 

 in the culture strains than the effect of merotomy. 



CONCLUSIONS. 



1. Merotomy has no effect other than the effect that may be 

 mechanically produced by the operation itself on the number of 

 micronuclei of Pleurotricha. 



2. Animals with more than the normal number of micronuclei 

 and less than the normal number of macronuclei may occur in 

 laboratory strains of this animal as well as among merozoa. 



ACKNOWLEDGMENTS . 



I am indebted to Dr. G. N. Calkins for suggesting this study to 

 me and for assistance, also to Dr. George A. Baitsell for the 



