GENETIC TYPE AND THE ENDOCRINES 335 



definite fashion. This fact may mean that the related pe- 

 culiarity of the pituitary is the primarily inherited character, 

 while the structural derangements are secondary results due 

 to the failure in harmonious growth regulation by the gen- 

 etically modified pituitary gland. 



Slight structural disharmonies in pure stocks may often 

 be enormously increased by hybridization. For example, both 

 the bulldog and bassethound have a mild degree of looseness 

 and wrinkling of the skin, but hybrids between these two 

 stocks show an exaggerated degree of skin overgrowth far 

 beyond that attained by either pure breed. A careful observer 

 may frequently notice similar accentuations of characters in 

 the hybrids between human racial stocks. 



THE BULLDOG MODIFICATION IN COMPARISON WITH 



OTHER SHORT MUZZLED AND ROUND HEADED 



DISTORTIONS IN NON-RELATED BREEDS 



The bulldog-like breeds thus far considered have all orig- 

 inated either directly or indirectly within a limited region 

 of western Europe. These breeds not only show similarities 

 in their head features, but are more or less similar in many 

 of their general characteristics. For example, all are short 

 and stocky in body form, and have short, stiff hair, brindle 

 coloring, a tendency for lifting or erecting the ears, etc. It 

 is highly probable that the typical modifications in the features 

 of the head and skull in the English and French bulldogs and 

 in the Boston terrier have been derived from one original 

 complex or series of mutations which occurred somewhere in 

 their common ancestry. 



It was impossible to learn from a study limited to the skulls 

 of these three breeds whether the bulldog-like deformities 

 occurring in entirely unrelated dog breeds and other animal 

 species were of similar genetic complexity and developed 

 on the same modified pattern. It seemed very desirable to 

 extend the investigation to include other breeds which had 

 independently developed comparable bulldog distortions of 

 the old ancestral dog head pattern. 



