GENETIC TYPE AND THE EXDOCRINES 499 



the bulldog in many respects but, as the skeleton shows, the 

 bulldog proportions are modified by the influence of the hound. 

 During life the head of the animal appeared more bulldog- 

 like than does the skull. The skull shape is between that of 

 the Fj hybrid and the pure bulldog; it is not fully shortened, 

 but the mandible is undershot and projects in front of the 

 upper jaw. The thyroid section shows a histologic pattern 

 which is clearly intermediate in its expression. The follicles 

 are smaller than in the hound and more uniform in outline 

 than in the bulldog. The follicular epithelium is cuboidal 

 and of a higher type than that of the hound, but falls much 

 lower than in the bulldog. After studying a great number 

 of these hybrid thyroids one is surprised by the consistency 

 with which differences in the histologic quality seem to follow 

 definite variations in physical form, from the normal thyroid 

 pattern and hound type through many intermediate and new 

 conditions and on to the highly distorted thyroid picture 

 associated with bulldog physical type. This correlation is so 

 close that the histologic pattern of the thyroid may be fairly 

 well predicted after a careful estimate of the type balance 

 between the two breed stocks in the individual concerned. 



The relations between histologic patterns of the thyroid 

 and peculiar structural types as found in the hybrid genera- 

 tions of the bassethound-bulldog cross lend strong support 

 to the comparable findings recorded for the Boston terrier- 

 dachshund hybrids. The quality and degree of activity of the 

 thyroid gland is intimately associated with the development 

 and final expression of characteristic types. And as we shall 

 report beyond, the peculiar morphologic types have limited 

 and characteristic manners of behavior, and these functional 

 reactions are also correlated with definite thyroid patterns. 

 We shall still postpone any attempt to answer the question 

 of whether the thyroid gland is the controlling element in 

 determining structural types and behavior patterns; un- 

 doubtedly its secretion performs a most important function 

 in these directions. Current opinion inclines toward the so- 

 called thyrotropic hormone from the pituitary as the power 



