206 THE ZOOLOGIST. 



was Black like the present subspecies, and have only found 

 hybrids between the two in London, where the Black race 

 exists. 



All the three above-mentioned races are sometimes found 

 frequenting the same town, and, as previously stated, will breed 

 freely with one another, and prove their original identity. Thus 

 we often see, in a collection of specimens, Bats of this species 

 presenting every intermixed condition of fur which may occur 

 between the very black form and the pale white-bellied one. 

 Black Bats with white chests, paws, and sometimes whitish 

 whiskers are common, as well as yellowish brown examples with 

 blue-grey under surfaces. This is most noticeable in London, 

 where the docks are constantly receiving fresh supplies of the 

 different subspecies from the east, and which make their 

 homes about the Docks, Batcliffe Highway, and Thames Street. 

 I have examined every type from this one district of our 

 metropolis. 



I think that this species may very occasionally interbreed 

 with M. decumanus, but I have never seen an example, nor has 

 Mr. Douglas English, who has long kept both species, succeeded 

 in obtaining a cross. Melanic varieties of M. decumanus and 

 variations of the present species are constantly described as such 

 hybrids. 



The scientific reader may question the necessity of describ- 

 ing the foregoing as new subspecies without according similar 

 subspecific rank to the melanic variety of Mus decumanus, for 

 some time known as M. hibernicus. The answer to this is that 

 the dark form of the last named is not constant, nor has it 

 developed into a sufficiently extensive race, inhabiting a certain 

 area, of which we can take notice. After all, the difference 

 between a variety and subspecies is a most difficult one to 

 describe. All subspecies have their commencement in a slight 

 variation from the normal type, which is altered and developed 

 according to circumstances and local environment. When that 

 variation is small and sporadic in distribution it is called a 

 variety, but if a variation becomes well marked and constant, 

 and its members dominate a district, island, or area of land, as 

 in the various races of Mus rattus, I think we are entitled to 

 name its members as belonging to a subspecies. 



