VAEIATIONS DEPENDENT UPON AGE, ETC. 43 



conjectures of Wieginann and Tenrminck. What other differ- 

 ences obtain, especially in external characters, can as yet be 

 only conjectured. It is to be hoped, however, that we shall 

 not have long to wait for detailed accounts of the external 

 characters of the adults of both sexes. 



FIG. 3. Odobcemis rosmarus, 9- 



INDIVIDUAL VARIATIONS, AND VARIATIONS DEPENDENT 

 UPON AGE. That a wide range of individual variation obtains 

 in this species is sufficiently evident from an examination of 

 even a limited series of skulls. These differences have been 

 noted in considerable detail by Frernery, Wiegmann, Stannius, 

 and Jaeger, as will be presently noticed more in detail in pre- 

 senting the general history of the species. Still greater differ- 

 ences, of course, result from differences of age. These collect- 

 ively, as will be noted later, have formed the basis of several 

 nominal species. All the Pinnipeds appear to be subject to a 

 wide range of variations of this character, and none more so than 

 the Walruses. These affect to a considerable extent the general 

 proportions of the skull, and especially the form and relative 

 development of different bones. These latter differences are 

 best seen in comparatively young skulls, since most of the 

 sutures close at a rather early age. Among these variations 

 are especially noteworthy those of the nasal bones, the inter- 

 maxillaries, and the frontals, and to a less degree those of the 

 base of the skull. The crests and ridges for muscular attach- 



