GENETIC TYPE AND THE ENDOCRINES 339 



misfits, such as dental malocclusion, are common among these 

 hybrids in both the first and second generations, and more 

 serious maldevelopment of the face has proved fatal at the 

 time of birth to some individuals of the second generation. 

 Here again, as in the bulldog, the head condition in the care- 

 fully bred and selected Brussels griffon is so complex in its 

 genetics that the best specimens are rarely completely homo- 

 zygous for the entire complex; hence, the variability in head 

 structures among the members of the F x generation. 



In general behavior, the F! hybrids show a variety of 

 reaction combinations derived from both parent breeds. They 

 are very nervous and restless and almost constantly on the 

 run, thus resembling somewhat the jumpy behavior of the 

 griffon; but at the same time they are extremely shy and 

 snappy towards people, and in this characteristic resemble 

 more closely the dachshund. 



Three F l bitches have whelped five litters of second gen- 

 eration, Fo hybrids. The litters contained six, three, eight, 

 four, and eight puppies, a total of twenty-nine. About half 

 of these lived to maturity. Four of the litters contained 

 one or more maldeveloped and grossly deformed puppies 

 which were dead at birth. The small litter of three was 

 the only one without a maldeveloped specimen, but since 

 it was so small it is very probable that defective fetuses had 

 died in utero before term. The deformities chiefly involved 

 head structures, early arrests of the extremities tending 

 toward amelia, with delayed development and lack of hair at 

 birth. 



Four Fo hybrids are shown in plate 64 (figs. 7-10), and 

 seven others are shown in plates 65 and 66. As will be recalled 

 from the discussion in a previous section, these F 2 individuals 

 have long, intermediate and short legs, and the majority 

 have long, rough hair. They are peculiarly susceptible to 

 mange infection and to rickety bones in spite of careful diet 

 and vitamin feeding. The latter reactions indicate a defective 

 and disturbed assimilation of calcium which cannot always 



