 The karyotype includes 40 chromosomes , with a fundamental number of 40 major chromosomal arms and resembles that of other members of the A. boliviensis group . Head and body length is 93 to 196 mm ( 3 @.@ 7 to 7 @.@ 7 in ) , averaging 158 mm ( 6 @.@ 2 in ) ; tail length is 46 to 83 mm ( 1 @.@ 8 to 3 @.@ 3 in ) , averaging 66 mm ( 2 @.@ 6 in ) ; hindfoot length is 18 to 25 mm ( 0 @.@ 71 to 0 @.@ 98 in ) , averaging 23 mm ( 0 @.@ 91 in ) ; ear length is 12 to 21 mm ( 0 @.@ 47 to 0 @.@ 83 in ) , averaging 14 mm ( 0 @.@ 55 in ) ; and body mass is 13 @.@ 0 to 38 @.@ 0 g ( 0 @.@ 46 to 1 @.@ 34 oz ) , averaging 21 @.@ 6 g ( 0 @.@ 76 oz ) . Like other members of the Akodon boliviensis group , individuals of Akodon spegazzinii continue to grow in adulthood . 
