No. 5S5] SHORTER ARTICLES AND DISCUSSION 575 



n generations of each particular type of mating. We have the 

 following values, where n denotes the nuniher of ancestral gen- 

 erations concerned, or. as Jennings puts it, the number of suc- 

 cessive inbreedings which have taken place. 



Type of Mating Coefficient of Inbreeding 



Raymond Pearl 



AN ATTEMPT TO PRODUCE MUTATIONS THROUGH 

 HYBRIDIZATION 



There is no more interesting problem to the experimental 

 evolutionist than the one relating to the cause or causes of the 

 origin of mutations. Until we are able to solve this problem we 

 can only accept what the gods give in our breeding experiments. 

 When a mutation arises it is usually a simple process to produce 

 a pure stock. By mutation is meant any deviation from the 

 normal type which reappears in some of the descendants. In 

 the following experiment most of the abnormalities that were 

 found never reappeared in the offspring. 



My experiments have been confined to the fruit fly, Drosophila 

 am/*, Innliila. a species kept for years "under cultivation" at 

 Columbia University. This species lias proved to be very plas- 

 tic, throwing off great numbers of mutant forms. At the sug- 

 gestion of Dr. T. H. Morgan I crossed some of these mutants 

 with wild stock of the same species from widely separated locali- 

 ties in order to test whether through hybridization mutations 

 arise in greater numbers than in inbred stock. 



The idea that new forms arise from crossing more or less 

 closely related species is an old one. One finds many references 

 in Darwin's works to this conception. For instance, in the 

 " Origin of Species " Darwin says: 



