162 PROF. W. H. FLOWER ON THE ELEPHANT SEAL. [Jan. 4, 



offset of the northern, because the only other known species of the 

 Cijstophori)i(e is also northern." 



Now it seems to me that if we are to accept the presumption 

 that they are distinct upon geographical grounds alone, we must bid 

 adieu to what little still remains to us, after the revolution of the 

 last twenty years, of our conception and definition of a species. 

 For how long in time and how far in space must two branches of 

 one stock of animals be separated in order to constitute a claim to 

 specific distinction? I should answer this question by saying, only 

 either when they have become so far physiologically differentiated 

 as no longer to interbreed (a point on which it is, of course, ex- 

 tremely difficult to get evidence), or when permanent recognizable 

 differential structural characters have been established. Until we 

 are sure that they are either physiologically or morphologically 

 distinct we have no grounds for separating them. In fact, by 

 doing so, we are concealing or ignoring a most important zoological 

 fact, viz. that inider certain circumstances members of a group may 

 become and remain for a long period of time isolated from the parent 

 stock without appreciable variation from the original type taking 

 place. Show any character in which the one has departed from 

 the other, however small, so that it be constant and universal, 

 then the case is altered, and it becomes a subject for consideration 

 whether the amount of variation is sufficiently great to be consistently 

 admitted as specific. But even this stage does not appear to be yet 

 reached in the case of the northern and southern Elephant Seals. 



The evidence upon which Dr. Peters has based the four supposed 

 species of southern Elephant Seal, viz. leonina, falklandica, probo- 

 scidea, and heryueleiisis, is still more shadowy ; but these were only 

 put forth by him as suggestions of possibilities, not as ascertained 

 facts. 



V.S. Since the greater part of the above was written, I have heard 

 from my friend Prof. Turner of Edinburgh that he has in his hands 

 for description the skeletons of a male and of a female Elephant Seal 

 from Kerguelen, and a skull of a large male from Heard Island, 

 brought home by the 'Challenger' Expedition, The latter, Mr. 

 Moseley informs me, he selected as one of the largest out of hundreds 

 which lay on the beach at the time of the 'Challenger's' visit, Feb. G, 

 1874 ; it is, however, considerably smaller than the specimei? 

 described above, having a condylo-premaxillary length of 20 inches 

 (483 niillims.) and an extreme length of 19 inches (.o08 millims.). 

 It is to be hoped that this large additional material will soon be 

 made available for reference. A good figure of the skull of an adult 

 female is at present an especial desideratum. 



