10 THE COMMON RATS 



form a strictly homozygous population, even from the standpoint 

 of color, since in subsequent crosses with pigmented forms they 

 give offspring with different color markings according to their 

 several latent characters. On the other hand it may be fairly 

 said that as yet we have no evidence for any correlation of the 

 somatic characters so far studied, with those slight differences 

 in gametic composition of the common albino strain which we 

 can recognize. It is to be noted moreover that the difficulty 

 which thus appears in the case of the albino rat repeats itself 

 for other mammals also, and therefore it does not constitute a 

 peculiarity of this animal. 



classification: references 



Alston, 1879-1882. Blasius, 1857. Doncaster. '06. Erxleben, 1777. Geof- 

 froy, 1812. Gesner, 1551. l'lsle, 1865. Linnaeus, 1758. 1766. Lloyd, '12. Mil- 

 lais, '05. Miller, '10. Mudge, '10. Pallas, 1778. Rehn, 1900. Topsell, 1658. 

 Trouessart 1881, 1897, '10. Tullberg, 1900. 



EARLY RECORDS AND MIGRATIONS OF THE COMMON RATS 



The common wild rats in the United States usally live in 

 close association with man. There are two species of these, both 

 of which have been introduced from Europe. These are Mus 

 rattus (Linnaeus, 1758; 1766 = Mus rattus rattus, Millais, '05) 

 together with its gray form, Mus alexandrinus (Goeffroy, 1812 ; 

 = Mus rattus alexandrinus, Millais, '05) and Mus norvegicus 

 (Erxleben, 1777 = Mus decumanus, Pallas, 1778). This last 

 species is our common gray, brown or Norway rat. In addi- 

 tion to these, all of which are wild, there is a fourth form — the 

 albino rat (Mus norvegicus albinus) a variety of Mus norvegicus 

 (Hatai, '07) which is known at present only as a domesticated 

 strain (Donaldson, '12 b). 



Mus rattus — the house rat — the first species described in west- 

 ern Europe, is probably indigenous to India. 1 As now found, 



1 Fossil remains of the rat (Mus rattus) are reported in the pliocene in Lom- 

 bardy (Cornalia, 1858) and in the quaternary at Molina di Anosa near Pisa (For- 

 syth Major) and again from the pleistocene cave deposits of the island of Crete 

 (Bate '12). This species appears in glacial times (Diluvialzeit) and in associa- 

 tion with man in the remains of the Lake dwellers in western Germany and in 

 Mecklenburg (Blasius, 1857). It is reported also from the diluvial deposits in 

 Bohemia (Woldfich, 1880). 



