GEOGRAPHICAL DISTRIBUTION 5 



The ancestral house mouse, from the present-day species 

 of which the main breeds of the fancy are derived, is un- 

 doubtedly of Central Asiatic origin. The date of its first 

 appearance in Eocene times and its subsequent expansion 

 may only be conjectured in terms of numerous millennia. 

 From the region of its early development it made its way to 

 the habitable portions of Europe, Asia, and northern Africa, 

 perhaps often as a stowaway in early human migrations. 

 At the present time the species Mus musculus is represented 

 in the old world by several interbreeding species and their 

 natural varieties. In northern Africa and Syria the pale, 

 white-bellied M. musculus gentilis is found. M. musculus of 

 southeastern Europe is in general darker than that of north- 

 ern Europe, and it seems to be the darker animal that be- 

 came established in Mexico and South America through 

 colonization by South Europeans, whereas the lighter form 

 is more common in the United States and Canada. 



The Asiatic Mus bactrianus group is lighter and more deli- 

 cate than the European M . musculus, but breeds freely with 

 it. Fancy breeds of mice often partake of blood of both 

 types, while the Japanese waltzing mouse of the fancy may 

 be derived (158, 59) solely from the bactrianus of China or 

 Tibet. 



Mus bactrianus (or wagneri (55)) ranges from Persia to 

 China. The general type of bactrianus blends into the short- 

 tailed M. bactrianus gansuensis of Mongolia and into the 

 long-tailed M. bactrianus kakhycncnsis in Indo-China and 

 the Malay peninsula (4). 



The species Mus musculus proper shared with the Euro- 

 pean his recent conquest of the globe, and was uninten- 

 tionally transported on ships or among merchandise to all 

 habitable regions including the Asiatic seacoast normally 

 within the range of the bactrianus group. 



This internationalization of the mouse has been so recent, 

 and complete isolation has been so rare, that few distinct 

 varieties have been able to develop and persist as such in 

 nature. However, where some isolation has been afforded, 



