4 THE COMMON RATS 



norvegicus as well as to the Albino (M. norvegicus albinus or 

 var. Albino), sometimes designated the 'white' rat. 



As will be pointed out in the section on The Early History 

 of the rat, there is one more complication in this connection. 

 Through an error, unfortunately perpetuated by some of the 

 natural histories, the common Albino has been described as an 

 Albino of the house rat Mus rattus. 



It thus happens that in some of the papers cited it is reported 

 that the observations had been made on Mus rattus or ratus 

 (sic), the word albino being sometimes added sometimes 

 omitted. In a few instances it is impossible to determine 

 whether M. rattus is used for the Albino or whether the house 

 rat was really studied. 



In forming a judgment oh these cases it must be kept in mind, 

 that for the last half century the house rat has been rare and 

 hard to obtain both in western Europe and in the northern 

 United States, so that unless the author gives good evidence 

 for the name he has employed, it becomes highly probable that 

 he was working with some form of the Norway. For these 

 reasons it has been found most convenient to include also in 

 Part I all the references to the house rat (Mus rattus). 



CLASSIFICATION AND NOMENCLATURE OF THE COMMON RATS 



Up to 1881 Mus (Linnaeus, 1758) was used as the generic 

 designation for both the rats and mice. In 1881 Trouessart 

 proposed the subgenus Epimys for the larger forms, the rats, 

 reserving Mus for the smaller forms, the mice Mus musculus 

 being the type. In 1910 Miller established the use of Epimys 

 for the rats. By the law of priority however Epimys must in 

 turn be displaced by Rattus (Fischer, 1803) as pointed out by 

 Hollister ('16). 



In the pages which follow however the designation Mus has 

 been retained for the rat as the older term is well understood, 

 while the new terms Epimys and Rattus are at present gen- 

 erally unfamiliar. 



