4.14 



THE AMERICAN NATURALIST 



[Vol. LIV 



viving Paramecin, found that a few were characterized by the 

 presence of three contractile vacuoles instead of two, the normal 

 number. Several of these animals were isolated and became the 

 progenitors of the multivacuolate race studied by Hance (2). 

 In speaking of the cytology of the race Hance mentions the 

 great difficulty experienced in staining the micronucleus and 

 states that ' ' the depression in the macronucleus where the micro- 

 nucleus usually lies is frequently visible but it appears quite 

 empty." He decided, however, that there was one micronucleus 

 present. 



The greater viability and the slightly larger size of this race 

 as compared with the wild races led to its use for class work 

 Having occasion, during November, 1919, to filter about four 

 hundred cubic centimeters of classroom culture densely popu- 

 lated by this race of Paramecium the writer fixed the animals so 

 obtained in warm Schaudinn's sublimate alcohol and subse- 

 quently stained them with Delafield's hematoxylin. On ex- 

 amination it was discovered that in none of the individuals 

 could a micronucleus be found. This observation in itself was 

 not conclusive since the seeming absence of the micronucleus 

 might have been due to faulty technique. The same material 

 was stained with borax carmine and the absence of the micro- 

 nucleus as a staining body was confirmed. Later four different 

 fixatives were used and the material stained with Carmalum 

 and in no ease was the micronucleus found. Material was then 

 fixed daily from a series of four cultures for periods ranging 

 from two to four months. Throughout this period the character 

 of the Paramccia remained constant in that no multivacuolate 

 animal possessed a micronucleus. 



For obtaining pure lines of amicronucleate animals with 

 which to make further observations twenty multivacuolate indi- 

 viduals were isolated. Some of the progeny of each of these 

 were stained in aceto-carmine and in each case the microuueleiis 

 was absent. The question as to the identity of the multivacuo- 

 late race and the amicronucleate race then arose. The fact that 

 the progeny of twenty multivacuolate individuals showed no 

 micronueleus supported this supposition. A number of slides, 

 made before the discovery of the multivacuolate race by Hance, 

 were found in the Laboratory by Doctor D. H. Wenrich, to 

 whom the writer is greatly indebted for his constant interest, 

 valuable advice, and criticism throughout this preliminary work. 

 Both micronucleate and amicronucleate individuals are to be 



