204 



The Journal of Heredity 



addition of a chromosome as large as 

 the Y or one of the rods. 



It is hardly profitable to speculate 

 further on what has happened in the 

 two cases just cited until genetical 

 evidence is availal)le, for as far as we 

 can see, only breeding experiments will 

 lead to the solution of the problem. 



No experiments involving exactly 

 this situation are being carried out at 

 present, so far as we know, but there 

 are others in progress which are suffi- 

 ciently similar to give promise of sug- 

 gesting the answer. In Figure 4 cer- 

 tain of the diagrams are emphasized 

 by stippling. These are the types 

 now involved in genetical studies. 

 They include two of the types just 



considered — F and J. And they also 

 include types A and M, which likewise 

 involve dififerences in the sex-chromo- 

 somes. In neither of these cases are 

 the two species concerned very close 

 relatives, but if chromosomal homo- 

 logies can be established in these cases, 

 as seems possible from present indica- 

 tions, the interpretations thus provided 

 may be applicable to other cases as 

 well. 



The above questions serve to illus- 

 trate some of the features which 

 genetical studies are designed to clear 

 up. A more detailed discussion will 

 be given in connection with the gen- 

 etical data. 



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