1883.] NATURAL SCIENCES OF PHILADELPHIA. 26Y 



less importance, and if we once qnit these well-marked and most 

 natural primary divisions we shall, I believe, open up questions 

 as regards the remaining regions which it will not be easy to set 

 at rest. There runs tlirough Prof. Heilprin's paper a tacit assump- 

 tion that there should be an equivalence, if not an absolute 

 equality, in the zoological characteristics and peculiarities of all 

 the regions. But even after these two are united, there will 

 remain discrepancies of almost equal amount among the rest, 

 since in some groups the Neotropical, in others the Australian, 

 far exceed all other regions in their specialt3^ The temperate 

 and cold parts of the globe are necessarily less marked by highly 

 peculiar groups than the tropical areas, because they have been 

 recently subjected to great extremes of climate, and have thus 

 not been able to preserve so many ancient and specialized forms 

 as the more uniformly warm areas. But, taking this fact into 

 account, it seems to me that the individuality of the Nearctic 

 and Paloearctic regions is very well marked, and much greater 

 than could have been anticipated; and I do not think that natur- 

 alists in general will be induced to give them up by any such 

 arguments as are here brought forward. 



"Alfred R. Wallace." 



Reply to the preceding : — 



" Permit me to make a few remarks relative to Mr. Wallace's 

 criticism (Nature, vol. xxvii, p. 482) of m}^ paper on ' The Value 

 of the Neai'ctic as one of the Primary Zoological Regions.' 

 Briefly stated, it is maintained in the early portion of this paper 

 (1) that the Nearctic ' and Pahiearctic ftiunas taken individually 

 exhibit, in comparison with the other regional faunas (at least 

 the Neotropical, Ethiopian and Australian), a marked absence 

 of positive distinguishing characters, a deficiency which in the 

 mammalia extends to families, genera, and species, and one 

 which, in the case of the Nearctic region, also equally (or nearly 

 so) distinguishes the reptilian and amphibian faunas; (2) that 

 thi§ deficiency is principally due to the circumstance that many 

 groups of animals which would otherwise be peculiar to, or very 

 characteristic of, one or other of the regions, are prevented fromi 



' In the paper under consideration, I have given what appear to me sutis- 

 factory reasons for detaching ce'tain portions of the Southwestern United 

 State's from the Nearctic (my Triarctic), and uniting them with the 

 Neotropical region. 



