Functional histology of the integument of the thin-spined porcupine, Chaetomys subspinosus

This study examines the functional histology of the thin-spined porcupine's (Chaetomys subspinosus (Olfers, 1818)) quills and integument, and compares them with the North American porcupine (Erethizon dorsatum (Linnaeus, 1758)) equivalents. Erethi-zon quills disseminate warnings to potential predators. An olfactory warning is generated by sebaceous glands of the lower back, disseminated by osmetrichial specializations of lower-back quills. Chaetomys skin lacks functional sebaceous glands, and generates no warning odor. Erethizon quills also carry a visual warning, effective even in dim light. Chaetomys quills carry no warning color. The straight, stiff quills of Erethizon are tipped with one-way barbs and can be elevated to 90 degrees. A protective col-lagenous spool at the base of the quill prevents back-stabbing on impact. Chaetomys quills lack barbs and the basal collagenous spool is poorly developed. The quill shafts are wavy and angled at the base, allowing them to act as shock absorbers during a fall from a tree. Nevertheless, Chaetomys quills of the head and shoulders can be elevated to 90 degrees to function as stabbing devices. Major defensive quills of Erethizon protect the back; in Chaetomys, the front. Though both species have 1-3 arrector muscles, they differ in the details of quill stabilization. The Chaetomys quill surface has regional cuticular patterns, of which the distal, longest region is highly pitted. The function of the pitted region remains a mystery.