We thus see how generally throughout the two higher vertebrate classes, and with some reptiles, the dermal appendages are erected under the influence of anger and fear. The movement is effected, as we know from Kolliker’s interesting discovery, by the contraction of minute, unstriped, involuntary muscles,[417] often called _arrectores pili_, which are attached to the capsules of the separate hairs, feathers, &c. By the contraction of these muscles the hairs can be instantly erected, as we see in a dog, being at the same time drawn a little out of their sockets; they are afterwards quickly depressed. The vast number of these minute muscles over the whole body of a hairy quadruped is astonishing. The erection of the hair is, however, aided in some cases, as with that on the head of a man, by the striped and voluntary muscles of the underlying _panniculus carnosus_. It is by the action of these latter muscles, that the hedgehog erects its spines. It appears, also, from the researches of Leydig[418] and others, that striped fibres extend from the panniculus to some of the larger hairs, such as the vibrissae of certain quadrupeds. The _arrectores pili_ contract not only under the above emotions, but from the application of cold to the surface. I remember that my mules and dogs, brought from a lower and warmer country, after spending a night on the bleak Cordillera, had the hair all over their bodies as erect as under the greatest terror. We see the same action in our own _goose-skin_ during the chill before a fever-fit. Mr. Lister has also found,[419] that tickling a neighbouring part of the skin causes the erection and protrusion of the hairs.