628 MURIDA:—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 100 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, 11; 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 
1 J. L. Bonhote, 27 /7¢. 
2 L, E. Adams, 47S. 3 Lantz, of. cit., 15. 
4 Newton Miller, Amer. Nat, xlv.. 623, 1911; C. E. Wright (in Millais, ii, 
230) found twenty young in a nest in a mole’s fortress in Northamptonshire ; 
C. H. Nash (Adams, zz /z.) 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 Fie/d (op. cit., 15), but at Bombay the pregnant females of 12,000 
specimens examined showed an average of 81, and a maximum of fourteen 
embryos (Etiology and Epidemiology of Plague, Calcutta, 1908, 9; and Lantz, of. _ 
ctt., 15). 
5 Newton Miller (of. cz¢.; and Mature, 26th October 1911), 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. /7ist.). 
7 L. Doncaster and F. H. A. Marshall, Journ. Genetics, 1, i. 18th November 
1910, 70. 
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