Issued October 28. 1907. 



U. S. DEPARTMENT OF AGRICULTURE 



BIOLOGICAL SURVEY— BULLETIN No. 31 



C. HART MERRIAM. Chief 



AN ECONOMIC STUDY OF FIELD MICE 



(GENUS MICROTUS) 



BY 



DAVII3 E. LAISTTZ 



Assistant, Biological Survey 



WASHINGTON 



GOVERNMENT PRINTING OFFICE 

 1907 



