No. 642] VARIATION IN REPRODUCTION 



9 



gave on the whole negative results ; they did not change. 

 Some of the investigators still insist that this is indeed 

 the outcome of all this work; that all cases seeming to 

 give other results are for one reason or another decep- 

 tive; that no hereditary variations occur; that evolution- 

 ary change has not been observed in this sort of repro- 

 duction—and presumably therefore in no other sort. 

 Thus, for example, argue Brierly (1919), and, in effect, 

 Victor Jollos (1921). 



On the other hand, in some of the organisms studied, 

 visible changes persisting from generation to generation 

 of uniparental reproduction have been observed. Even 

 in the first period of this sort of work, extremely rare 

 ''mutations " were reported by Barber in his work on 

 bacteria, an apparent single one by Lashley in Hydra; a 

 " bud variation " or two by Johannsen; and other iso- 

 lated cases occurred. In the second period of the work, 

 as a matter of observational fact, whatever the interpre- 

 tation, it is certain that in the lowest Rhizopoda: in Dif- 

 fliigia, in C entropy xis, in ArceUa; in tlie infusorian Stylo- 

 nychia, and in certain abnormal strains of Paramecium, 

 as studied in our laboratory at tlic Johns Ifopkiiis Uni- 

 versity, there arise in uniparental rcpiM hirtioii. diaiiges 

 affecting both physiological and structural characters; 

 changes that may be very slight, or of great extent; that 

 are passed on to later generations in uniparental repro- 

 duction. By selection and breeding of the changed indi- 

 viduals, stocks are isolated which differ persistently from 

 the stock with which the work of breeding began. In this 

 way might well arise the diverse biotypes found in nature 

 to occur within a species, in these organisms. Something 

 similar was found by Stout in the propa.uati(.n of certain 

 plants by cuttings. 



Again, among the 16 strains of Chuhxvra, snh.jcrtr.l by 

 Banta to selection for a ]ihysiologlcal characteristic, one, 

 and only one, showed persisting- alterations, accumulated 

 by the silective p)roce>s, so that from the single strain, 

 two continuously diverse strains were produced. Jollos 



