GENETIC TYPE AND THE ENDOCRINES 295 



cally complex in origin, being influenced in its expression by 

 some factors which tend to be dominant for the normal head 

 type and others which tend to be recessive. If all the bulldog 

 head features were recessive to the normal, the F 1 hybrid 

 would not show a shorter and heavier head than that of the 

 shepherd. In breeding the F x hybrid back to the shepherd, 

 these modifications of the long head type are almost com- 

 pletely lost. The great variety in degree of expression for 

 bulldog head or the difference among phenotypes shown by 

 the hybrids from the backcross of the Fi with the bulldog, 

 clearly indicates the presence in the underlying genotype of 

 a complex of factors which are essential for the fully expressed 

 bulldog head. 



The analysis of the bulldog head and of the general char- 

 acteristics associated with it, necessitates the study of an 

 abundance of hybrid material which could only be derived 

 from a more productive breeding stock than the shepherd- 

 bulldog cross has proved to be. On this account we resorted 

 to the far more prolific cross between the bulldog and the 

 bassethound. So far as our experience goes, this cross has 

 enormous advantages in such a study, and on this basis the 

 general analysis of the bulldog characteristics is considered 

 in the following chapter. 



GENETIC CONSTITUTION AND EXDOCRIXIC ABNORMALITY 



AS FACTORS IN THE GROWTH AND STRUCTURAL 



MODIFICATIONS OF THE ENGLISH BULLDOG- 



BASSETHOUND HYBRIDS 



In a previous section, we considered the inheritance and 

 development of the extremities in the cross between the Eng- 

 lish bulldog and the bassethound. It will be recalled that the 

 bassethound is of normal dog size, possessing a normal head 

 of the hound type, a well proportioned body, and a long, 

 straight tail, while the extremities are very short with extreme 

 aehondroplasic deformities. The legs of this animal furnish 

 one of the most striking cases of sharply localized chondro- 

 dystrophy in an otherwise normal skeleton. The behavior 



