A \K\V SPECIES OF PAR. \MECIUM (P. MULTIMICRO- 

 XUCLEATA) EXPERIMENTALLY DETERMINED. 1 



J H. POWERS AND CLAUDE MITCHELL. 



On September 27, 1909, I received from Dr. Powers two sample 

 cultures of Paramecia with the request that I investigate them 

 as to type and purity of culture. To this end I first killed, fixed, 

 mounted and examined 1,000 individuals. They proved to be 

 neither typical Paramecium cdiitJatnni nor Paramecium anrclhi, 

 although most of their characters differed but little from these 

 well-known types. Their length ranged between 144 and 288 /z. 

 Their anterior end was a little blunter and the posterior end a 

 little more pointed than even in P. caudatitm. The cytoplasm 

 was more dense and more opaque. Their chief difference, 

 however, from hitherto described types of Paramecia lay in the 

 matter of the micronucleus, for, instead of the single micronucleus 

 of P. caudatum or the two micronuclei of its variety P. a arc/ in, 

 there is a number of very small bodies, evidently micronuclei, 

 ranging in diameter from about .7 to 1.15 // (Fig. 3). The char- 

 acteristic position of micronuclei is fully retained, these bodies 

 lying either in slight grooves or in shallow impocketings of the 

 macronucleus. Like the micromiclei of other types, these deli- 

 cate bodies are always surrounded by a nuclear membrane. 



Of the I ,OOO individuals examined 875 distinctly showed 

 Iroin two to six of these small micronuclei, 1 24 showed apparently 

 no micronuclei whatever, while one appeared at first to possess 

 a micronucleus of the type found in P. cditdatitni. This single 

 instance, however, turned out upon careful study to be a ca>e 

 in which a detached fragment of the macronucleii> chanced to 

 simulate in size and appearance the regular micronucleus. As 

 to the 124 which appeared \\iihout micromiclei, entire degenera- 

 tion of these bodies may h.i\ e been possible, but it is more prob- 

 able that a slight oxerstain obscured I hem, especially when 

 lying behind the macronucleus; the same explanation is doubt- 

 studies from the Zoological I.al.oi .itoiy, the I 'nivrrsity n\ \VI,i .i^ka, No. 101. 



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