Races of Paramecium. 541 



the races had died out completely, the effects of this environmental 

 action would appear to be permanent. Thus, study of the effects 

 of the environment are likely to be most deceptive when made 

 upon organisms not positively known to be pure as to race. The 

 only safe method for such study is to begin with a single individual, 

 from which all the specimens studied must be derived, and to take 

 the most rigid precautions against accidental introduction of indi- 

 viduals of another race. 



It is very probable that study of reactions to stimuli in the differ- 

 ent races, and of other physiological matters, would show diversi- 

 ties among the different races in these respects. Such a study will 

 probably be made later. 



6. Relation of the races to the described species of Paramecium 



What relation have the races here described to the various 

 named species of Paramecium, aside from caudatum and aurelia? 

 Are possibly some of these named species based on observation of 

 these races? 



A review of the various species of Paramecium that have been 

 described shows that in these races we have to do only with the 

 two species P. aurelia and P. caudatum. 



Ehrenberg ('38) informs us that up to his time no less than 

 fifty-six specific names had been given under the genus Parame- 

 cium. But when we recall that under this generic name the old 

 observers signified merely small animals that were, as Miiller 

 (1786) defines it, "inconspicuous, simple, pellucid, membrana- 

 ceous, oblong, " it will be understood that most of these had noth- 

 ing to do with what we now understand by the genus Paramecium. 

 Indeed, only a single one of these fifty-six, P. aurelia Miiller, 

 belonged to our present genus. Miiller (1786) had attributed 

 five species to the genus, under the specific names oviferum, 

 marginatum, aurelia, chrysalis, and versutum; all but aurelia 

 belong elsewhere. 



Ehrenberg ('38) did but little better. He attributed eight species 

 to Paramecium, under the specific names aurelia, caudatum, 

 chrysalis, colpoda, sinaiticum, ovatum, compressum, milium. 



