THE GRAY BAT. 309 



of multiplication is such that, if none were killed, 

 a pair of rats might at the end of two years have 

 descendants to the tune of ninety thousand ! 



But, although figures illustrating this point may 

 appeal to some as vaguely amusing, the actual 

 results attained should provoke tears rather than 

 laughter. Though not fully developed till six 

 months old, a gray rat under suitable conditions 

 may begin to breed at the end of five weeks. The 

 first litter, however, is a small one, numbering, 

 probably, not more than three. Thereafter the 

 number of litters per year, and the number of 

 young per litter, are decided entirely by the cir- 

 cumstances in which the rat lives. If the season 

 is normal, neither too hot nor too cold, and food 

 is plentiful, the gray rat will produce six litters 

 annually, the young numbering from eight to 

 twenty at a birth. Working on a basis of a wide 

 range of statistics, we arrive at the fact that a 

 normal gray rat living under normal rat conditions 

 in other words, the average rat successfully 

 brings into the world forty-eight children per year. 

 Accepting the predominance of bucks which seems 

 always to exist, this would give us twenty female 

 children to the year, each of which may begin to 

 produce its equally fertile offspring at the end of 

 five weeks, and thus ad infinitum. 



The young are blind for fourteen days, and if 

 the male rat plays any part in their existence, it 

 is by bringing that existence to a sudden end, to 

 his own epicurean satisfaction. The young leave 

 the nest at the end of about eighteen days, 

 and at this age are to be seen abroad at all 

 hours, little larger than mice, and readily falling 

 victims to any kind of trap that may be set for 

 them. 



