146 MODES OF RESEARCH IN GENETICS 



effects of inbreeding upon the progeny. This 

 restriction has been deliberate. The primary pur- 

 pose of what has preceded is to make some con- 

 tribution to the methodology of the study of the 

 important problem of inbreeding. It has seemed 

 desirable to emphasize the fact that in the investi- 

 gation of the problem of inbreeding in general 

 there are three elements, which from the stand- 

 point of the logic of the case, are totally distinct 

 and separate. These are : 



1. The logical and mathematical characteristics 

 of a system of mating of organisms such that the 

 individual has fewer different ancestors than it 

 would have had under the operation of any other 

 system of mating. Having proper regard for the 

 meaning of words, such a system of mating, and 

 that alone, can logically be called inbreeding. 



%. The necessary consequences in respect of the 

 Mendelian constitution of the individual which 

 must follow the continued operation of systems of 

 mating which are inbreeding. 



3. The physiological effect on the individual 

 consequent upon its having been produced through 

 the operation of a system of mating which is 

 inbreeding. 



The first of these three phases of the problem 

 is the one attacked in the preceding sections of 

 this paper. In these the attempt has been made 

 to show in the clearest way of which the writer is 

 capable that inbreeding is a mode or system of 



