GENETIC TYPE AND THE ENDOCRINES 151 



differences in quality of the endocrine glands in different 

 dog breeds give ns almost ideal material on which to investi- 

 gate the significance of these relations. 



The differences in skull shapes, cranial capacities and facial 

 arrangements exhibited among the dog breeds are of special 

 interest as correlated with the behavior of the individuals, 

 since milder degrees of the same expressions in human beings 

 are frequently associated with modifications in behavior and 

 mental reactions. It is well known that dogs of different 

 breeds behave in widely different ways, and many of the 

 instinctive reactions found in one breed may be entirely dif- 

 ferent or actually lacking in another. Whether these devia- 

 tions in behavior are consistently associated with definite 

 differences in head forms, and whether a given head form 

 is the developmental result of a characteristic endocrine 

 quality or balance, are questions that can be studied to 

 greater advantage in contrasted dog types than in either 

 human beings or other mammalian species. 



With such considerations in mind, it seemed very desirable 

 to analyze the differences among dog skulls in some detail 

 and with as much accuracy of measurement as could be 

 attained. After the many skull differences had been estab- 

 lished, their hereditary significance among the hybrids of 

 contrasted breeds was carefully followed. We further made 

 an extensive study of both gross and microscopic conditions 

 of the endocrine glands from all these animals. In the follow- 

 ing sections of this report the findings for the various glands 

 and their possible relation to the structural and functional 

 modifications found among the pure breeds and their hybrids 

 will be discussed. Finally, some of the instinctive and con- 

 ditioned behaviors accompanying the various head types 

 will be recorded in an effort to determine in what ways 

 structural changes may be correlated with modified types 

 of functional behavior. Experimental modification of the 

 endocrine balance and its influence on behavior in the dif- 



