IN VIVO Observations of Skin Appendages in the Bat Wing

Abstract

The anatomical patterns and tile physiological activity of the sebaceous and apocrine glands and associated structures were observed in vivo in the wings of bats. Over five hundred skin appendages in more than 100 bats were studied using light microscopy. The pilosebaceous unit includes, besides the hair, its follicle and sebaceous glands, a limiting tissue sheath that envelops the unit. The sheath contains a number of contractile fibers that normally exhibit rhythmical contractions of approximately 4/min and press upon the enclosed sebaceous glands. The action may be similar to that described earlier for the piloerector muscle in other mammals and suggests a possible active mechanism in sebum excretion. It is also seen that sebum excretion is preceded by the formation within the sebaceous glands of oil-like drops that may eventually fill the entire gland. An apocrine gland is associated with many of the pilosebaceous units. Each resembles an elongated balloon composed of an inner layer of secretory cells surrounded by a single cell layer of contractile tissue. Its tortuous duct opens at the skin surface close to the follicular orifice. An occasional forceful contraction of the gland followed by peristaltic contractions of the duct expresses the watery contents to the skin surface. The bat wing preparation affords a natural skin window wherein the appendages and associated structures can be directly observed in vivo and studied without injury or alteration, either physical or chemical.