GENETIC TYPE AND THE ENDOCRINES 289 



The mating between these two dogs whelped three hybrid 

 puppies, two females and a male, all of which lived to adult- 

 hood. A photograph of one of the F x bitches is shown in 

 plate 54 (fig. 3). She was a handsome animal of strong, 

 mastiff-like appearance and a quite vicious attitude toward 

 other dogs. She is taller and larger in body than the bulldog 

 and stockier than the shepherd. Her head, as the photograph 

 shows, is much like that of an English mastiff and not very 

 different from the German boxer dog; it is heavier and 

 shorter than that of the shepherd, but has only a mild ex- 

 pression of the typical bulldog pattern. This is one of the 

 few F! hybrids in the experimental kennels which even a 

 person familiar with dog breeds is invariably unable to diag- 

 nose for hybrid origin. There are almost no features which 

 clearly suggest the shepherd dog, and the stocky features 

 resemble more closely those of breeds other than the bulldog. 

 The three F t shepherd-bulldogs were remarkably alike in 

 general appearance. 



The male F t died at maturity and so no second generation 

 hybrid offspring were produced. However, a sister, 659 9 , 

 was successfully used for the backcross with both parent 

 stocks, and the resulting hybrids have supplied some definite 

 indications of the genetic relations between the extreme 

 bulldog skull and the normal long German shepherd type. 



The behavior records of these two F x shepherd-bulldog 

 sisters are particularly interesting. One, 658 9 , remained in 

 the kennels for 3 years without whelping a puppy although 

 she was mated several times with productive studs of record. 

 This bitch also missed several oestrous periods. Her sister, 

 659 9 , now more than 6 years old, had at 4 years of age 

 produced five whelps of eight, eleven, ten, twelve and nine 

 puppies, a total of fifty offspring. Of this number she suc- 

 ceeded in rearing twenty-seven to over 3 months of age, which 

 is in general a good record. 



The whelping behavior of 659 9 , however, was far from 

 calm. She was shy and wild in her reactions. More care and 



