376 GEOGRAPHICAL DISTRIBUTION, Chap. XL 



identically the same ; but they are much oftener speci- 

 fically distinct, though related to each other in a most 

 remarkable manner. 



This brief abstract applies to plants alone : some 

 strictly analogous facts could be given on the distribu- 

 tion of terrestrial animals. In marine productions, 

 similar cases occur ; as an example, I may quote a 

 remark by the highest authority, Prof. Dana, that " it 

 is certainly a wonderful fact that New Zealand should 

 have a closer resemblance in its Crustacea to Great 

 Britain, its antipode, than to any other part of the 

 world." Sir J. Eichardson, also, speaks of the re- 

 appearance on the shores of New Zealand, Tasmania, 

 &c, of northern forms of fish. Dr. Hooker informs 

 me that twenty-five species of Algae are common to 

 New Zealand and to Europe, but have not been found 

 in the intermediate tropical seas. 



It should be observed that the northern species and 

 forms found in the southern parts of the southern hemi- 

 sphere, and on the mountain-ranges of the intertropical 

 regions, are not arctic, but belong to the northern tem- 

 perate zones. As Mr. H. C. Watson has recently re- 

 marked, " In receding from polar towards equatorial 

 latitudes, the Alpine or mountain floras really become 

 less and less arctic." Many of the forms living on the 

 mountains of the warmer regions of the earth and in 

 the southern hemisphere are of doubtful value, being 

 ranked by some naturalists as specifically distinct, by 

 others as varieties ; but some are certainly identical, 

 and many, though closely related to northern forms, 

 must be ranked as distinct species. 



Now let us see what light can be thrown on the fore- 

 going facts, on the belief, supported as it is by a large 

 body of geological evidence, that the whole world, or a 

 large part of it, was during the Glacial period siniulta- 



