at 50 days of age , chihuahua , mexico mice ( latitude of origin 27 degrees n ) and south dakota , u.s.a. mice ( 44 degrees n ) kept in the 10l:14d photoperiod had reduced gonadal and seminal vesicle weights and a lower spermatogenic index than corresponding mice kept in a 14l:10d photoperiod .
C0037717
south dakota
C0041703
u.s.a