474 CHARLES R. STOCKARD AND E. M. VICARI 



tary resemble more closely the glands from the dachshund 

 stock (pi. 87) than the F x hybrid (pi. 88). 



The backcross pituitaries supply strong evidence in favor 

 of the deductions drawn from the F 2 glands above, that is, 

 that the physical form and type of the individual is corre- 

 lated with the histologic pattern and cellular nature of the 

 pituitary gland, and that in line with the widely contrasted 

 physical types of the Boston terrier and the dachshund there 

 is a correspondingly strong divergence between the histologic 

 patterns of the pituitary glands. Among the F- and back- 

 cross hybrids, a consistent relation between the specific types 

 and the histologic qualities of the pituitary glands is ex- 

 pressed. AVe have also seen in a previous section that a 

 similar correspondence is definitely maintained between the 

 dachshund and Boston terrier body types and the microscopic 

 patterns of the thyroid. 



Linkage between a characteristic thyroid pattern and a 

 given bodily type was not interpreted as a causal relation- 

 ship. Are we then, from the foregoing evidence, justified 

 in interpreting the relation of the pituitary quality to the 

 physical types of the individual as being causal in nature? 

 If the physical type of the dog is a developmental result of 

 the pituitary quality, shall we also consider the character- 

 istic pattern of the thyroid gland in a given type as simply 

 another feature under the pituitary influence? Or, does the 

 thyroid gland independently share, along with the pituitary, 

 the responsibility for the characteristically modified body 

 types f A satisfactory answer to these questions is still 

 difficult, even on the basis of the extensive evidence already 

 considered. An examination of the conditions in still another 

 member of the endocrine series is therefore necessary if we 

 are to find other possible clues to further interrelationships. 

 And further, it is most essential that we survey these prob- 

 lems in other modified and contrasted breeds and their 

 hybrids so as to secure comparisons for the dachshund-Boston 

 terrier records just presented. 



