X.] DUAL ORIGIN OF GROUPS. 381 



With a quotation from Mr G. H. Carpenter's interesting 

 paper 1 on this subject, the present volume may be fitly closed. 

 After describing the inhabitants of the Mitchelstown Cave, in 

 Ireland, the author writes that the spring-tail (Lipurd] "is hardly 

 to be separated from a species found in the caves of Carniola, and 

 the Sinella is almost identical with one inhabiting the caves of 

 North' America ; while the spider is apparently the same as a cave- 

 dweller from the Mediterranean district of southern France, which 

 probably occurs in the North American caverns also. Had we to 

 do with animals of the upper fauna, these results, though highly 

 interesting, would not be without parallel in species already 

 known.... But the occurrence of cave-dwelling species with so 

 wide a range is a truly remarkable phenomenon. The caves 

 cannot be of any great geological age. Any possible geographical 

 connection which would permit the migration of subterranean 

 animals between southern Europe and Ireland, or between Ireland 

 and North America, seems altogether out of the question within 

 any period during which the fauna can have been specifically 

 identical with that of the present day. The only conclusion is 

 that from ancestors, presumably of the same genus, which took to 

 an underground life in such widely-separated localities, the similar 

 conditions of the caves have evolved descendants so similar that, 

 when compared, they cannot or can hardly be specifically distin- 

 guished from each other. Should the identifications stand the 

 test of a comparison of types, we shall have proof that the inde- 

 pendent development of the same species, under similar conditions, 

 but in widely-distant localities, has taken place. It must be 

 granted, however, that cave-conditions are so marked and excep- 

 tional, that it might not be safe to argue from them as to what 

 may have occurred in the upper world." 



Although the author of this passage is perfectly correct in his 

 statement that there is a vast difference between cave-life and 

 open-air life, yet if animals which appear to belong to one and the 

 same species can be proved to have had a dual origin in the one 

 case, it can scarcely be considered impossible that similar instances 

 may occur in the other. And if such dual origins exist among 



1 Irish Naturalist, Vol. IV. pp. 25 35 (1895). 



