242 THE ZOOLOGIST. 



elusive proof that there was only one Colchican Pheasant, and 

 the numerous phases of plumage were variations. Unfortunately, 

 this theory is completely upset by the fact that true mules or 

 hybrids, the offspring of undoubted separate species, are often 

 fertile. Thus, take two such totally distinct species of Ducks, 

 the Pintail (Dafila acuta) and the Mallard {Anas boseus). If 

 these be crossed, the result of such a union is fertile. These 

 hybrids in their turn then cross with either species, producing 

 offspring. Yet no one could possibly claim the Mallard and 

 Pintail as one species ! This digression is necessary to explain 

 how hopelessly bewildering is the making of a species. It has 

 often surprised me when dealing with zoological problems to 

 find how little climate is taken into account in the attempt 

 to explain variations in different forms. But, again, climate 

 usually tends not one whit to alter a species found in totally 

 different quarters of the globe. One might go on ad infinitum 

 dividing and subdividing the different races of Salmonidce, when 

 the results would be far from satisfactory. For my own part, I 

 see nothing very remarkable in Mus sylvaticus and Mus flavicollis 

 inhabiting the same area, though at this some people have 

 expressed surprise. What I maintain is : that Mus flavicollis 

 is gradually but surely in many places ousting Mus sylvaticus, 

 and establishing itself as a species. On the other hand, it is, in 

 some districts, either dying out or migrating to fresh quarters. 

 I am inclined to take the former view, for this reason. I have 

 picked up several dead and dying specimens of Mus flavicollis 

 (some of the latter were already " fly-blown "), but have very 

 rarely seen a dead — natural death being the cause — Mus sylva- 

 ticus. In the year 1907 I never failed night after night to trap 

 half a dozen or more Yellow-necked Mice in my garden. During 

 1908 I never caught a single example, and this year — 1910 — 

 Yellow-necks are at a premium, for, up to the present date, 

 May 19th, I have only taken one. Barrett-Hamilton* has given 

 us an excellent monograph of Mus sylvaticus and its subspecies, 

 and, whether we all agree or not with his classification, this 

 must, for the present, remain our standard work on these Mice. 

 All who are interested in small mammalia would do well to read 

 the conclusions of this painstaking naturalist. My claims for 



* Proc. Zool. Soc. Lond. 1900. 



