VIL] SPECIES AXD SPACE. . 165 



tant points of the southern hemisphere, of species which, 

 though distinct, belong to genera exclusively confined to 

 the south, is a more remarkable case. Some of these spe- 

 cies are so distinct that we cannot suppose that there has 

 been time since the commencement of the last glacial period 

 for their migration and subsequent modification to the ne- 

 cessary degree." Mr. Darwin goes on to account for these 

 facts by the probable existence of a rich antarctic flora in a 

 warm period anterior to the last glacial epoch. There are 

 indeed many reasons for thinking that a southern conti- 

 nent, rich in living forms, once existed. One such reason 

 is the way in which struthious birds are, or have been, dis- 

 tributed around the antarctic region: as the ostrich in 

 Africa, the rhea in South America, the emeu in Australia, 

 the apteryx, dinornis, etc., in New Zealand, the epiornis in 

 Madagascar. Still the existence of such a land would 

 not alone explain the various geographical cross-relations 

 which have been given above. It would not, for example, 

 account for the resemblance between the Crustacea or fishes 

 of New Zealand and of England. It would, however, go 

 far to explain the identity (specific or generic) between 

 fresh-water and other forms now simultaneously existing 

 in Australia and South America, or in either or both of 

 these, and New Zealand. 



Again, mutations of elevation small and gradual (but 

 frequent and intermitting), through enormous periods of 

 time waves, as it were, of land rolling many times in 

 many directions might be made to explain many difficul- 

 ties as to geographical distribution, and any cases that re- 

 mained would probably be capable of explanation, as being 

 isolated but allied animal forms, now separated indeed, but 

 being merely remnants of extensive groups which, at an 

 earlier period, were spread over the surface of the earth. 

 Thus none of the facts here given are any serious difficulty 

 to the doctrine of " evolution," but it is contended in this 



