The porcupine in North America is considered as belonging to but the one species _dorsatum_, although there are seven subspecies. The most common subspecies found in the Southwest is _epixanthum_ (Greek _epi_, upon, and _xanthus_, yellow), sometimes called “yellow-haired” porcupine. The porcupine is unique among North American mammals in bearing the sharp quills which are perhaps its most interesting feature. Certainly they are responsible in large part for the unusual life history of this misunderstood animal. Quills are no more than greatly modified hairs, and in sorting through the various types of pelage on a porcupine’s back, a few examples will be found which are intermediate between the hair and the quills. This does not mean that coarser hairs gradually turn to quills. Each follicle produces hair or quill, as the case may be, for the life of the animal. A quill consists of three well-defined parts: a solid sharp tip usually black in color; a hollow shaft, which is white; and a root similar to that of a hair. [Illustration: porcupine] The sharp tip is smooth for a fraction of an inch, but from this point on, it is covered with a great number of closely appressed barbs. These can be felt by rubbing the quill the “wrong” way between thumb and forefinger. It has been found that these barbs flare away from the surface, when the quill is immersed in warm water. It seems natural that they would do the same when embedded in warm, moist flesh. At any rate, quills are always difficult to extract, and if left in the victim they penetrate ever more deeply until they may pierce some vital organ and cause death. In other cases, they have been known to work entirely through body or limb and emerge on the opposite side. This is due to muscular action of the victim, some movements tending to force the point farther, the barbs at the same time effectively preventing any retreat. Below the barbs the tip of the quill flares to join the shaft. Pure white and opaque, this portion is used by Indians to form decorative bands of quill work on the fronts of buckskin vests and jackets. This part is also hollow, and before removal of a quill from the flesh is attempted, a little of the end should be cut off. This collapses the shaft and makes extraction somewhat more easy, but very little less painful. Actually there is little excuse for a human to become involved with one of these mild-tempered creatures, but sometimes dogs are badly hurt in encounters with them.