Variation and Taxonomic Significance in the Sebaceous Caudal Glands of Pocket Mice (Rodentia: Heteromyidae)

Abstract

Gross and microscopic studies of tails of adult heteromyid rodents reveal a specialized sebaceous glandular area in the ventral side and centered a quarter to a third the distance from the tail base, in species of Perognathus. Although well developed only in this genus of the family, the caudal gland shows marked species differences and possibly as well, variation related to sex and reason. However, many more specimens are needed in order to substantiate the latter points. Possible significance of the caudal glands in olfactory communication and behavior seems likely but is not yet supported by observations or experiments. Restricted to North and Middle America, and centered in the South- west, is the rodent family Heteromyidae, containing the genera Het- eromys, Liomys, Perognathus, Dipodomys and Microdipodops. The species of the genus Perognathus, the pocket mice, present an assem- blage of forms that is poorly understood taxonomically and phylo- genetically. As in many genera of small animals, the frequently ar- bitrarily chosen and standard characteristics and measurements may be suspected of not being as pertinent or diagnostic as others, which may be less obvious due to their manifestations primarily in histology, cytology, biochemistry, physiology or behavior. Specialized glandular areas of the skin may be considered to be of particular value in studies of generic, specific and subspecific differentiation in many groups of mammals including the Heteromyidae. I wish to report here the discovery of a special caudal glandular area in Perognathus, and to comment in a preliminary way on its tax- onomic distribution and variation. MATERIALS AND METHODS. This study is based in part on gross inspec- tion of many specimens, but primarily on serial, histological cross- sections of the tails of 33 pocket mice (Perognathus), representing 15 of the known 26 species according to Hall and Kelson (1959). Nearly all of the specimens for histological study were collected in June and July. Serial sections for comparative purposes were also prepared from tail segments of species of the other heteromyid genera. From nearly all of the animals, segments were taken at the tail base and about a fourth to a third the distance from base to tip. The latter area was sug-