1938 Volume 8 Issue 3-4 Pages 408-419
All the species of Peromyscus so far studied except P. eremicus have 48 chromosomes. One subspecies of P maniculatus was found with 52 chromosomes. Evidence is found supporting Painter's base number 48 for mammals, but no explanation is offered for the 58 chromosomes found in P eremicus.
Evidence is found in favor of fragmentation as a method for increasing chromosome numbers within a species. This process may be in progress in P maniculatus at the present time.
Almost complete harmony is found between the results of the breeding tests made by Dice and the results of the cytological study made here.
A suggested relationship between various species of Peromyscus is offered based upon cytological evidence.