14 Records of the Indian Museum. [\oh. Ill, 



explanation, but always in this particular order: 

 Length, tail length, length of hind foot (from heel to 

 longest toe, excluding the clawj, length of ear (the 

 greatest length). In this way the measurement of a 

 common rat would be shown as 175, 200, 30, 20. 



2. By the length of a skull is meant the distance from the 



condyles to that part of the premaxillse which projects 

 between the incisor teeth. The molar series has 

 been measured at the roots of the teeth where they 

 spring from the sockets. In measuring skulls, '5 mm. 

 has been usualh' regarded as the indivisible unit. 

 This seems rather a coarse method, but it was found, 

 when the unit was "25 mm., that measurements of the 

 same skull, taken by two careful observers, did not 

 often agree. Some workers split the millimetre into 

 ten equal parts ; they accomplish this feat presumabl}' 

 by using ordinarily well made dividing compasses, 

 the points of which together rareh^ measure less than 

 •3 mm. They are recommended to repeat the mea- 

 surements of one skull day after da}^, and to observe 

 the variety of the results obtained. 



3. The term " new character " is used here to denote par- 



ticular characters which are only present in some few 

 members of a race, — for example, about one in every 

 thousand rats has a white-tipped tail. This was 

 noticed in Mus rattus, Mus concolor, Gunomys and 

 Bandicota. The phenomenon of a white-tipped 

 tail is spoken of as a new character. Occasionally 

 this particular character is common. Several Mus 

 concolor from one district show it. Other exam.ples 

 of new characters are melanism, albinism, albiventral- 

 ism and caudal bicoloration. There is an undoubted 

 similarity in the method of occurrence of these 

 characters among rats, hence one term is applied to 

 them. A rat showing a new character is a sport, 

 though some sports show more than one such character. 

 By a white-bellied rat is meant one in which the 

 belly, chest, throat, lower jaw, and the inner side of 

 the limbs is covered with pure white fur ; this charac- 

 ter is very common among Oriental rats. 



4. The term "family group" lias been frequently used. 



It was found that the rats of one house were always 

 more closely alike than an equal number of rats 

 taken from different houses in the same town; this 

 is not surprising, but it was sometimes found that 

 the rats from one house or set of burrows were very 

 closely alike, not only in colour, but in proportion 

 of body and skull, and that they were collectively 

 different from the mean of the mixed race of which 

 they formed a part. Rats showing new characters 



