446 Prof. J. Steenstrup on the Character of the 



of a country may often be very different in the different classes 

 of animals of which its famia consists, inasmuch as not only 

 may the animals of the surrounding sea or the coast-fauna 

 belong to another geographical region than the land animals, 

 but even of the latter, again, one class, by reason either of its 

 mode of life, or of a stronger or weaker faculty of motion, may 

 sometimes present striking differences from tlie rest. Hence 

 it is perfectly natural that an author who seeks to explain the 

 reasons for the present distribution of animals upon the sur- 

 face of the earth should choose rather to treat geographically 

 each class of animals by itself, and to seek to ascertain and de- 

 termine with regard to each class of animals the particular 

 country's zoogeographical character. This is just what Andrew 

 Mm'ray has done, in his great work, furnished with 101 fine 

 maps, ' The Geographical Distribution of Mammals.' But if 

 we determine the geographical character of a country or of a 

 large island in this manner, from a single class, in this case 

 from the mammalia alone, we certainly expose ourselves to 

 great errors, especially when this class is very poor in species, 

 or when its species are not very well known. A striking 

 example of this is presented by the above-mentioned work, as 

 regards Iceland, inasmuch as the indigenous terrestrial mam- 

 malian fauna of this island, which has a surface of nearly 

 2000 square miles, can only be said to consist of a single spe- 

 cies ; and this single species therefore is that which in this case 

 is to decide whether Iceland belongs, in a zoogeographical 

 sense, to Greenland and North America, as the author sup- 

 poses, or to the Europajo-Asiatic region, as we have hitherto 

 believed, whether forming our judgment upon the characters 

 of the class of mammalia or of the other classes of terrestrial 

 animals. 



This single species therefore plays, in the important pro- 

 blem of the origin and diffusion of animals, a part so decisive 

 that a single species of animal can hardly have it to fulfil in 

 any other point. Murray has, indeed, perfectly felt this *, and 

 he has not come lightly to his result, but, on the contrary, after 

 ample consideration ; but, in order to carry this on in a correct 

 manner he seems partly to have wanted a sufficient knowledge 

 of the animal in question, and partly not to Iiave perfectly 



* At p. 2G7, for example, Murray says: — "In speaking above of the 

 long-tailed field-mouse, I reminded the reader of the nature of its habi- 

 tation with some exactness, because it is the only guide we have to en- 

 able us to determine whether that species does or does not exist in Iceland, 

 or whether, as I suppose, it is the lemming which has been mistaken for it 

 there — a fact which, as the reader hnmvs, mud Juice rather an important 

 bearing on the past geological history of that part of the northern hemi- 

 sphere." The italics are mine. 



