Histological differences in the thyroid glands from two subspecies of Peromyscus maniculatus

Many of our native mammals have never been investigated carefully from tlie standpoint of either gross or microscopic anatomy, although they undoubtedly present instructive differences from the usual laboratory animals or from one another. There is the added fact that even closely related species, or races within the same species, exhibit coiisiderable differences in color and proportions, apparently because of an adaptation to the very different ciiviroiimeiits wliicli are included within even small areas of western America. Since such color aiid proportional differences have also been shown to follow operative removal of the thyroids and parathyroids or tlie feeding of thyroid substance (Hammett, '23 ; Horning and Torrey, '27), tlie histological inrestigatioii of these organs in closely related types should present facts of coiisiclerable vdiic. As a preliminary study of a mammalian type which has already attained some prestige in genetic investigations, we are presenting a comparison of the histological appearance of the th:~oid glands in two subspecies of the deer mouse, Peromyscus manicnlatas rubidus and 1'. m. soiioriensis. Our observations are based iipoii fourteen adult specimens of the former species (seven males and seven females), and thirteen adult specimens of the latter (nine males aiid four females). The specimeiis of rubidus, a longtailed dark-colored type,