402 



University of California Publications in Zoology [Vol. 21 



TABLE 7 



Eelative Numbers of Animals Less Than One Year Old and Animals More 



Than One Year Old Collected in September, 1918, in 



Contra Costa County, California 



numbers than do those animals more than one year old. This same 

 conclusion \yas arrived at by Grinnell and Dixon (1918, pp.. 631-632) 

 regarding this species in January from a study of specimens taken 

 in that month. In January, however, as pointed out by these authors, 

 the ratio of animals more than one year old to animals less than one 

 year old increases as the month advances. January marks the begin- 

 ning of the breeding season. The application to be made of this fact in 

 carrying out control measures as usually practiced is obvious. As 

 stated by Grinnell and Dixon {loc. cit.), it is : ". . . . the need of 

 poisoning in the spring rather than in the fall, when part of the breed- 

 ing stock may be stowed away out of the reach of poisoned grain. 

 It is a question, too, whether or not a dormant animal, in which respira- 

 tion is extremely slow, would be fatally injured by a fumigant before 

 the latter would be dissipated." 



To separate the series of skulls into two age groups it was necessary 

 first to group the skulls according to sex. The series of female skulls 

 corresponding in age to that of males showed a lesser degree of develop- 

 ment of the ridges, crests, and processes. This is not alone confined 

 to height and sharpness of the crests but to their longitudinal exten- 

 sion as well. The greater length of the sagittal crest in males as a 

 result of the greater degree of convergence of the parietal ridges is a 

 case in point. One hundred and forty-six male skulls less than one 

 year old have an average condylo-basal length of 53.7 mm., while the 

 average of the "same measurement for 103 female skulls of the same age 

 is 52.1 mm. The average weight of the skull — minus lower jaw and 

 hyoid — for 35 skulls of each sex of apparently the same age was found 

 to be 4.1 grams for males and 3.9 grams for females. 



