J. H. POWERS AND CLAUDE MITCHELL. 



describe these at the present time save in so far as they relate 

 to the present discussion. Many of the nuclear changes were 

 erratic and possibly pathological: Macronuclei greatly enlarged, 

 micronuclei unchanged, or sometimes apparently absent, or again 

 enlarged, even more in proportion than the macronucleus, and 

 sometimes divided. 



Among the large mass of such material, stained, mounted and 

 examined, I discovered a very few instances of individuals with 

 two typical micronuclei. In fission these micronuclei divided 

 simultaneously and normally. The number of these individuals 

 was very few, probably not exceeding one to several thousand, 

 but they confirm, to some extent, Calkins's observation that P. 

 aurelia may arise from P. caitdatum. 



Among the different types of variants I sought assiduously 

 for examples of P. multimicronucleata. But none of the exact 

 type were found. Evidently this type is farther separated from 

 P. caudatum than is P. aurelia. A considerable number of indi- 

 viduals were found however which showed an approach to P. 

 multimicronucleata, in that the micronucleus was divided, usually, 

 again, into but two bodies, perfectly normal in appearance, but 

 much smaller than the typical micronuclei of the genus, though a 

 little larger than those of the new type. This variant was one of 

 the most constant and frequent results of the changed diet. In 

 other characters, however, it did resemble closely P. multimicro- 

 nucleata or, for that matter, any recognized type of the genus. 

 I regard it merely as an instance of the well-known law that a 

 powerful stimulus to variation applied to any species brings out,, 

 not only new characters, but characters of existing allied species 

 as well. The phenomena, to the writer, serve to confirm, rather 

 than to refute, the specific independence of the new type. But 

 they are of interest in themselves as showing possible lines of 

 experiment leading to nuclear variation. In the present instance 

 it seemed especially worth while to record them, and indeed this 

 is the chief reason for the entire studs', in thai Paramecium is- 

 more and more being made the subject of extensive experimental 

 research. So far, little of this study has had regard to other 

 than external characters, but this admitted limitation must soon 

 be remedied, and to this end it is eential that we kn<>\\ the type c 



