J. H. POWERS AND CLAUDE M1TCHELF.. 



have often failed to procure, from wild slock, pure cultures of 

 P. caudatum. A portion, usually the bulk, and frequently the 

 whole, of any culture obtained from pond or river water would 

 turn out to be of this multimicronucleate type. 



I did not at first recognize the minute micronuclei. I regarded 

 the individuals, which careful and elaborate technique showed 

 to be lacking in the typical micronuclei of P. caudatum and P. 

 ditrelia, as degenerates in the sense of Maupas' contention. As 

 however the hypothesis of the degeneration of the micronucleus 

 became more and more discredited, I reexamined mounted slides 

 of these Paramecia under high magnifications, with the result 

 that the minute bodies in question were visible in every case. 

 That this type of Paramecium was not related to degeneration 

 was further shown by the fact that many pure cultures, unlike 

 those with which Mr. Mitchell has labored so assiduously, have 

 been vigorous and strong grow r ers. I may further mention the 

 fact that in several very large aquaria supplied with running 

 water and a small amount of fresh meat added occasionally, 

 this type of Paramecium apparently maintained itself continu- 

 ously for several years. As often as the organic matter was 

 supplied the animals would multiply and appear in vast swarms 

 in the corners and protected portions of their space; whenever 

 examined they proved of this type and of this type only. 



The existence of an undescribed species of Paramecium seems 

 improbable. The protozoa are considered of universal distribu- 

 tion, and Paramecium is the most-studied genus in existence. 

 Nevertheless much of the study of mircoorganisms is superficial; 

 many have failed to develop a suitable technique, easy as this is, 

 for the certain demonstration of micronuclei ; and as to the 

 hypothesis of universal distribution, it is certainly assumed much 

 further than it is proven. Thus, for the last six years, I have 

 made careful search among cultures derived from very numerous 

 wild stocks, for Paramecium of the aitrdni lype, i. e., with thr 

 well-known two micronuclei. But, aside from a very few isolated 

 individuals derived experimentally from P. caudal nm, not a single 

 example has been found. 



All in all, it seems that, in the light of Mr. Mitchell's results, 

 the type in question deserves specific rank, although this rank 



