82 



BULLETIN OF THE 



Sexual Differences. — The sexes differ in color, as already stated, in 

 the females being much lighter than the males, or grayer. In respect 

 to the skeleton they differ extraordinarily in the form of the pelvis, as 

 already described,* all the parts of which in the female are greatly reduced 

 in size, and instead of the pubic bones meeting each other posteriorly, 

 as they do in the males, they are widely separated. The innominate 

 bones are also much further apart in the females, and the bones forming 

 the front edge of the pelvis are less developed, so that the pelvis in the 

 female is entirely open in front. In consequence of the remarkable nar- 

 rowness of the pelvis in the male, the form of this portion of the skeleton 

 is necessarily varied in the female, to permit of the passage of the fetus 

 in parturition. As already remarked, no such sexual differences are seen 

 in the Phocidce. 



In respect to other parts of the skeleton, the absence of the great de- 

 velopment of the sagittal and occipital crests seen in the males has already 

 been noticed. The bones of all parts of the skull are much smaller and 

 weaker, especially the lower jaw and the teeth. The attachments for the 

 muscles are correspondingly less developed throughout the skeleton. The 

 most striking sexual difference, however, is that of size; the weight of 

 the full-grown females, according to Captain Bryant, being less than ONK 

 sixth that of the full-grown males. 



Differences resulting from Age. — The differences in color between the 

 young and the adult consist, as already stated, in the young of both sexes 

 during the first three or four months of their lives being glossy black, and 

 gradually afterwards acquiring the color characteristic respectively of the 

 adult males and females. In respect to the differences in the skeleton 

 that distinguish the young, I can only speak of the skull. In regard to 

 this a most striking difference is seen in the relative' development of 

 its different regions, as compared with the adult of either sex. The 

 two young skulls before me, said to be from specimens thirty-five days 



* In the comparison of the skeleton of the eared seals with that of Phoca ritulma 

 (above, p. 25 et seq.). 



