THE AMERICAN NATURALIST 



[Vol. LYI 



had thought to overthrow ; who came to scoff remained to 

 mourn. 



Such was, m the gross, the upshot of the first phase of 

 the study of uniparental inheritance ; of perhaps the first 

 ten years. But the matter could not rest here. This 

 work cleared the ground. It showed that 99 per cent, or 

 more of what had been called variation had nothing to do 

 with evolutionary change— a • conclusion which Mende- 

 lian study was reaching independently. Now it remained 

 to accept that fact, to take a new hold, to grapple with 

 the more difficult question: Is there yet an infinitesimal 

 residuum of evolutionary change? If we select the most 

 favorable organisms, and study them in most minute de- 

 tail for sufficiently long series of generations, shall we 

 indeed find that there are no persistent variations what- 

 ever? Such is the work that has in this field occupied, 

 with redoubled intensity, the last ten years. What are 

 the results of this second phase of the work? 



Some of the workers devoted themselves to observa- 

 tional breeding work on the passage of many generations, 

 accompanied by selection; others attempted to modify 

 the inherited characters by physical and chemical agents. 

 In the observational search for persisting alterations, 

 with the attempt to accumulate their results by selection, 

 we find, first, that many of the organisms studied have 

 as yet defied all attempts to find any inherited variations. 

 Such is the report of Ewing on his extended work with 

 aphids ; such is the case with the fungi studied by Brierly 

 (1920). Such is the case with most of the strains of the 

 infusorian Paramecium, studied in detail for long periods 

 by many different observers. Only in certain deformed 

 strains, and possibly in one or two other instances, has 

 the occurrence of persisting variation been observed in 

 animals living under the usual conditions. Such is the 

 case with the great majority of the strains of the Clado- 

 cera studied with such extraordinary thoroughness for 

 long periods by Banta (1921) ; out of 16 strains to which 

 selection was applied for many generations, all but one 



