468 CHARLES R. STOCKARD AND E. M. VICARI 



The striking contrast between the histologic patterns of 

 the pituitaries and the thyroids from the dachshund typed 

 Fo and the Boston terrier typed F 2 in the dachshund-Boston 

 terrier cross may be appreciated by comparing figures 1 and 

 3 with figures 2 and 4 in plate 89. More exaggerated differ- 

 ences in histologic patterns between endocrine glands would 

 be difficult to find. 



We have already seen from the consideration of thyroid 

 histology among different dog breeds that some breeds present 

 characteristic patterns which appear to be correlated with 

 their physical types. The parathyroids, as we shall see later, 

 also differ in their cellular arrangements, and here again 

 developmental arrests play a role in the formation of cysts 

 and tubular structures. For an understanding of the genetics 

 of size differences and skeletal modifications in the mammals 

 and man, these three endocrine glands the thyroid, pituitary 

 and parathyroids must be carefully considered for their 

 possible roles as intermediaries between the genie mutations 

 and the final structural modifications. Still further, since 

 there is evidence of an association between structural types 

 and behavioristic patterns, as examples of which are the 

 proverbial giant and dwarf psychologies which have long 

 been recognized, what role may the endocrinic complexes play 

 in these expressions? If all these are genuine relationships, 

 we may expect that when definite endocrinic modifications are 

 accurately correlated with specific structural expressions 

 these will indicate types of characteristic behavior. With such 

 knowledge, an understanding of the influences of endocrinic 

 diseases on instinctive and psychic reactions will be forth- 

 coming. 



Returning to the special consideration of pituitary histology 

 in the F 2 dachshund-Boston terrier hybrids, it must be empha- 

 sized that all the glands from such animals are not such 

 strong expressions of one or the other parent type as are the 

 two cases just presented. As will be recalled, the great 

 majority of these hybrids are intermediate in type, resembling 

 the Fj group, while a smaller number present various mixtures 



