GENETIC TYPE AND THE ENDOCKIXES 



251 



fact is altogether concealed by averaging" the F 2 skull indices ; 

 an average would fall close to that of the F u as recorded 

 in table 2. The standard deviation in this table is, however, 

 three times as large for the F 2 index as for the F,. 



SKULL INDEX 



UPPER FACIAL INDEX 



ABC D E F 



Text-figure 57. Dachshund-Boston terrier cross. Each vertical Line represents 

 an index based on exact measurements of the skull, and the same series of skulls 

 was used for the three charts. A, dachshund; B, Boston terrier; C, F 2 ; D, F 2 ; 

 E, baekeross of ¥\ with the Boston terrier; F, backcross of F 1 with the dachshund. 



When the F, hybrid is crossed back with the Boston terrier, 

 the skull index of the hybrid offspring is raised. The indices 

 for nine of these backcross hybrids range from 79 to 94. 

 They approach more nearly the Boston terrier skull index 

 than does the F 2 group, and eight are above the indices for 

 the F x s. 



Only one skull represents the total skull index for the 

 backcross of the F 1 on the dachshund. This skull is longer 

 than the F : parent but is -L- units higher than the index for 

 the dachshund skull. 



