14 Mr Alfred R. Wallace on some Anomalies 



the distribution of different groups, and of the probable 

 causes of such anomalies, it appears that the six regions of 

 Dr Sclater do approximately represent the best primary 

 divisions of the earth for natural history purposes. They 

 agree well with the present distribution of mammalia, birds, 

 reptiles, land shells, and very generally of insects also. The 

 cases in which they do not seem correct are those of isolated 

 groups in restricted localities. The greatest discrepancies 

 occur in groups which have at once great capacities for 

 diffusion, and little adaptability to change of conditions ; 

 and, in the case of plants, have probably been much in- 

 creased by what may be called the adventitious aid of the 

 glacial period and of floating ice. 



Of botanical distribution I have said little, from w^ant of 

 knowledge of that branch of the subject, and I can find no 

 detailed information bearing Idirectly upon the questions 

 here discussed, but what I have already mentioned. It is 

 much to be desired that some comj)etent botanist would 

 point out how far these regions agree with, and how far 

 they contradict, the main facts of the distribution of plants. 

 It seems evident that the various modes of glacial action 

 have produced much more effect on the migrations of plants 

 than on those of animals, and also that plants have, on the 

 whole, more varied and more effectual means of dispersal. 

 Still, if the views here advocated are true, the flora of each 

 region should exhibit a characteristic substratum of indi- 

 genous forms, though often much modified, and sometimes 

 nearly overwhelmed by successive streams of foreign invasion. 



My object in calling attention to the subject by this very 

 partial review of it, is to induce those naturalists, who are 

 working at particular groups, to give more special attention 

 to geographical distribution than has hitherto been done. 

 By carefully working out the distribution of allied genera 

 and closely connected groups of species, they could give 

 the amount of agreement or discrepancy with other groups 

 whose geography is best known, and furnish us with such 

 information on the habits of the species, as might help to 

 explain the anomalies which were found to occur. We 

 should thus soon accumulate a sufficiency of detailed facts 

 to enable us to determine whether these are the best pri- 



