GENETIC TYPE AXD THE ENDOCRINES 225 



the internal environment on developmental expression, but 

 they have supplied almost nothing to aid in the understanding 

 of the significance of the genetic constitution in determining 

 the responses. Do the constitutions of certain tissues force 

 them to give definite structural reactions in spite of various 

 internal modifications? For instance, must there always be 

 a genetic basis for the typical acromegalic modification as 

 seen in nature, or may this be experimentally induced in any 

 individual ! These and many other similar questions of serious 

 importance have not been answered with any degree of satis- 

 faction by experimenting with glandular ablations or hor- 

 monal applications. 



Human families, as has been frequently mentioned, may 

 possess modified structural features of the cranium and face 

 closely the same as are found among the dog breeds. It is 

 evident that a complete understanding of the nature and 

 origin of such peculiarities involves a careful analysis of 

 the genetic background along with a consideration of the 

 endocrine complications which may accompany these distorted 

 expressions. The most valuable material available for this 

 genetic and endocrinal analysis is found to be the long estab- 

 lished and carefully selected dog breeds of distorted types. 

 This fact has been previously emphasized in other connec- 

 tions. 



In attempting the analysis of head types and distortions, 

 we have employed several different crosses between highly 

 contrasted breeds. Thus we are able to determine whether 

 a given peculiarity arises in the same way in all cases or 

 breeds, and whether it behaves in similar genetic fashion for 

 all cross combinations. Whether or not the peculiarity is 

 irregular and highly variable in its genetic reactions or in 

 its expression is of much importance. 



For this study the Boston terrier, French bulldog and 

 English bulldog were selected as representing three different 

 and quite uniformly established degrees of bulldog modifica- 

 tion of the skull. 



