628 MURID^— EPIMYS 



when five weeks old, and no doubt wild does attain sexual 

 maturity long before they are really full-grown, Shipley states 

 that in Bombay sexual maturity is not reached until the weight 

 is at least loo grammes. 



The period of gestation is about twenty-one days/ and the 

 number of young in a litter is said to reach thirteen,^ fourteen,^ 

 or sometimes twenty ; * but many litters, especially those of 

 young females, are very much smaller, and sometimes consist of 

 a single young one only.^ Mr Cocks has records of twenty- 

 three litters ^ of pregnant does examined at Great Marlow and 

 Poynetts ; four of these contained 6 ; ten, 7 ; three, 8 ; two, 

 10 ; three, 1 1 ; and one, 12 — giving an average of nearly 8 per 

 litter. In one of 7 the foetuses were of two sizes ; 3, situated 

 at distal end of right horn, being very small. Two litters of 

 7 and 5 respectively were obtained from a rat with only one 

 ovary.' 



The young are as helpless at birth as those of other 

 murines, being blind, pink, and hairless, and with the ears 

 sealed down over the auditory meatuses. They are carefully 



' J. L. Bonhote, in lit. 



2 L. E. Adams, MS. s Lantz, op. cit., 15. 



* Newton Miller, Amer. Nat, xlv., 623, 191 1 ; C. E. Wright (in Millais, ii., 

 230) found twenty young in a nest in a mole's fortress in Northamptonshire; 

 C. H. Nash (Adams, in lit.) found a double nest containing two old and sixteen 

 young ones, and Owen Jones found thirty-four little rats in one nest. Seventeen and 

 nineteen embryos and twenty-two and twenty-three young in nests are quoted by 

 Lantz from the Field {op. cit, 15), but at Bombay the pregnant females of 12,000 

 specimens examined showed an average of 8-i, and a maximum of fourteen 

 embryos {Etiology and Epidemiology of Plague, Calcutta, 1908, 9 ; and Lantz, op. 

 cit., IS). 



6 Newton Miller {op. cit ; and Nature, 26th October 191 1), experimenting with 

 captive Common Rats, found the period of gestation to vary between twenty- 

 three and a half and twenty-five and a half days ; the rats breeding in every 

 month of the year. The female may produce five or six litters annually; 

 the number of young per litter averaging between ten and eleven, and ranging 

 between six and nineteen. One female produced seven litters in as many 

 months, and it was presumed that in cases where all the young perished 

 at birth there would be a dozen litters in the course of the year. The captives 

 devoured 50 per cent, of their young at birth, most, if not all, of these being 

 eaten by the females. Although full growth is not attained before the eighteenth 

 month, sexual maturity is reached in both sexes at least as early as the end of the 

 fourth month. 



* Inclusive of those published previously in Bucks ( Vic. Co. Hist). 



' L. Doncaster and F. H. A. Marshall, Journ. Genetics, i, i., i8th November 

 1910, 70. 



