i8 Records of the Indian Museum. [Vol. Ill, 



As the immature have not been excluded, there must be some 

 among those measuring 175 mm. which are not mature ; if these 

 had been removed the mean would be raised. Therefore, the mean 

 shown in the diagram is somewhat lower than the true adult mean. 

 The immature were included owing to the difficulty of sa^^ing 

 whether many of the smaller individuals were mature or not. It is 

 highl}^ probable that some of the specimens measuring 140 to 150 

 mm., in which the third molar is cut and even slightly worn, have not 

 stopped growing. Because of this, it was thought best to include 

 the measurements of all specimens received, and this has been done 

 not onl}' in the case of the Punjab rats, but in the case of all house 

 rats from other places when they have been received in sufficient 

 numbers. 



These measurements show that the house rats of the Punjab 

 hardly differ in length from the rats of Calcutta. Hossack's 

 measurements of ninety Mus ratius afford the only standard available 

 for comparison. The measurements of other writers are of ' ' types. ' ' 

 Hossack found pregnant rats of between 140 and 150 mm. length, 

 while among the ninety are six rats of over 190 mm. length ; he 

 states and repeats the statement ' ' gradation of size is simpl}^ one 

 of age." It is possible that his meaning is not expressed fully; 

 as it stands it is obviously- erroneous. A man of six feet four is 

 not alwa3^s very old ; moreover, Hossack's published figures con- 

 tradict his statement, for while the ninety" rats contain only six 

 individuals between 190 — 200, there are nine between 180 — 190, 

 and twenty between 170 — 180. These results are similar to those 

 obtained for Mus rattus in other parts of India, and if arranged 

 would show a similar diagram. 



The 500 measurements from the Punjab show that adult rats 

 vary from (about) 140 to 225. This is not evidence that the Punjab 

 race is larger than the Calcutta race, as the measurements were taken 

 in a slightly different wa}^ in the two cases ; moreover, they are of 

 500 Punjab rats and 90 Calcutta rats. However, it would not be 

 a matter for surprise if the Punjab rats w^ere somewhat larger. 

 The results of length measurements obtained from such different 

 places as the Punjab and Calcutta are therefore approximately 

 the same. The}^ will be compared with those from other parts of 

 India. 



Tail length. — There is some evidence that the mean of the tail 

 length in Punjab rats is less than that of the Calcutta race, also that 

 in the Punjab there are groups of rats in which this value is excep- 

 tionally low. At first sight Captain Dav3's's measurements show sur- 

 prising differences from those of the Calcutta race. Many are shown 

 as having the tail length less than the length. This is partly due to 

 the fact that the measurements were recorded by Davys from the first 

 ring of the tail, and not from the anus. On repeating some of the 

 measurements, but from the anus to tail tip after brief immersion in 

 spirit, it was found that the new values obtained were all about 7 

 mm. more than those of Dav^^s's records. The difference of course 

 varied with the size of the rat. In order to equalize the Calcutta 



