GENETIC TYPE AND THE ENDOCRINES 327 



more difficult of endocrine explanation is the fact that a 

 single hybrid individual may show symptoms of both types 

 of growth distortion, being dwarf in body size with an over- 

 growth of skin or other parts. 



The regulatory mechanisms for adjusting growths to nor- 

 mal size and form must be quite stably balanced among pure 

 breeds, or there could not be so large a majority of individuals 

 with fairly uniform measurements. It is difficult to believe 

 that the constitutional complex which tips this adjustment 

 towards gigantism and acromegaly is the same as that which 

 in an identical environment lowers it towards dwarfism and 

 chondrodystrophy. However, the occurrence of these con- 

 trasted patterns among the bulldog-bassethound second hy- 

 brid generation might indicate that the distortions of size 

 in both directions are the consequence of strange genetic 

 associations which arise in hybrid combinations. As pure 

 breeds, neither the bassethound nor the bulldog shows tenden- 

 cies toward giant or dwarf body size, and yet both breeds 

 have localized chondrodystrophy in their skeletons, along with 

 an excessive production of loose-fitting skin. Chondrodys- 

 trophy is commonly found among dwarf types, and over- 

 growth of skin is common among giant breeds. When dog 

 breeds carrying these two qualities are crossed, the hybrids 

 show new variations in total body size, and individuals both 

 larger and smaller than the parent types are produced. 



This is an entirely different phenomenon from inheritance 

 of breed size when large and small breeds are crossed. Breed 

 size in some cases is inherited in a very simple manner, 

 while in others it is more complex and the members of the F a 

 generation may be larger in size than either parent stock. 

 One of the simplest examples of size inheritance is the cross 

 between the full sized bassethound and the small dachshund. 

 Total body size in this cross follows a rather definite Men- 

 delian behavior. The F a hybrids are uniformly intermediate 

 in size when compared with the parent stocks, although they 

 are probably somewhat nearer the dachshund. The large 



