Journal of Agricultural Research voi. xxvu, no.s 
\ 
usually keep in perfect condition. Without plenty of water or dry earth 
the fur becomes oily and rough, but either water or sand removes the 
excess oil and leaves it light and fluffy. 
The nests are kept clean while in use and are abandoned when they 
get old and stale. New nests with soft linings are usually prepared a few 
days in advance for each litter of young, so that new nests or fresh 
linings are generally provided about every 20 days. 
Their little long green pellet-like excrements are more or less scattered 
along the trails and on the feeding grounds, but in the burrows or near 
the nests they are deposited in little heaps in out-of-the-way places. 
In the cages some corner farthest from the nest is usually chosen for the 
purpose, or sometimes the water dish is used as a urinal and the pellets 
are deposited in a corner or in another dish. In such case to keep the 
cages from becoming foul they have to be cleaned frequently and supplied 
with fresh sand or sawdust. As an experiment, outside receptacles were 
provided by placing a square tin can with a hole in the side large enough 
for the mice to enter from a corresponding hole in the side of the cage. 
An inch of sand in the bottom of this can gave an attractive little dark 
compartment which the meadow mice at once adopted and used exclus¬ 
ively for toilet purposes. As the cans merely hooked onto the outside 
of the cages and could be conveniently emptied and supplied with fresh 
sand every day or two, the cages were kept clean with little trouble. 
BREEDING HABITS 
It has long been known that these mice are very prolific breeders, 
specimens of females containing embryos, usually four to eight in number, 
being taken at all seasons. The mammae are arranged in four pairs, two 
of inguinal, and two of pectoral on four elongated mammary glands, and 
eight young should be the normal maximum number. 
FREQUENCY 
In captivity the young, if well fed, begin to breed when less than half 
grown, the females mating with older males when only 25 days old and 
having young when 45 days old, and the young males mating when only 
45 days old. The period of gestation is approximately 21 days, in one 
case 20 days and 17 hours. The breeding activities are practically con¬ 
tinuous* the females mating immediately after the birth of the young and 
producing litters of usually 4 at first, but when full grown, after the first 
or second litter, usually 6 or 8 at a birth. Seventeen consecutive litters 
of young have been produced by one female in captivity within a year— 
May 25, June 14, July 8, July 29, August 23, September 18, October 18, 
November 9, November 30, December 21, January 12, February 2, 
February 23, March 18, April 8, April 30, May 20—and then she showed 
no signs of being near the end of the breeding period, while several genera¬ 
tions of her young have busily followed her example, one of them, born 
on May 25, having produced 13 families of young, totaling 78 in number, 
before she was a year old. 
The number of young in a litter ranges from 2 to 9, and with the orig¬ 
inal pair, averaged 5, totaling 83 in 17 litters. At this rate of increase, 
allowing equal numbers of males and females and the young beginning 
to breed at 46 days old, the total increase from one pair, if all lived and 
bred, would be over 1,000,000 individuals at the end of a year. If all 
