Races of Paramecium. 545 



It would not be difficult to collect from the literature observa- 

 tions indicating the existence in Paramecium and other infusoria 

 of races differing in inherited characteristics. « One or two ex- 

 amples of this must suffice. Maupas, in his paper of 1888, says 

 that all the progeny of a single individual are alike morphologically 

 and physiologically (p. 176). Differences in rate of fission, etc., 

 do show themselves among different individuals of the same 

 species, but Maupas is convinced that in such cases we are deal- 

 ing with progeny of different original parents; that they belong, 

 in modern terms, to different "pure lines" with different racial 

 characteristics (pp. 203-204). In Onychodromus he finds heredi- 

 tary differences in the rate of fission, in different lines (pp. 220- 

 221). The same thing is observed in different lines of Leuco- 

 phrys (pp. 241-242). 



Gruber ('92) described "dwarfs" of Stentor coeruleus and Sten- 

 tor polymorphus (I have not been able to see the original paper). 



Enriques, after an extensive physiological study of " Colpoda 

 steini," discovered that this consists of two sets of individuals, 

 with permanent inherited differences of size ('08, p. 272). One set 

 consists of small individuals, which may readily be induced to 

 conjugate; the other of larger specimens, that do not readily 

 conjugate. On account of these differentiations in size and in 

 physiology, Enriques considers these to be distinct species. To 

 the larger race he gives the name Colpoda maupasi, while the 

 smaller retains the name Colpoda steini. (For full account of 

 these, see Enriques, '08a). It is to be noticed that the differ- 

 ences between these two species are of the same character as the 

 differences between two of our races of Paramecium of the aureha 

 group. The race k differs from the race i in size and in greater 

 readiness to conjugate. We might therefore distinguish these 

 as two different species. The chief objection to this is that the 

 number of such races is in Paramecium so great, and the differ- 

 ences between them often so slight, that the giving of separate 

 specific names to each w^ould confuse rather than clear the mat- 

 ter. There is the further possibility that the different aurelia 

 races may be found to interconjugate, giving intermediate forms; 

 this has not yet been observed. 



