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Show i02 i\IEANS O:P EXPRESSION of tho will; and this action must be looked at, 'vhen, occurring under the influence of anger or fear, not as a power acquired for the sake of some advantage, but as an incidental result, at least to a large extent, of tho sensorium being affected. The result, in as far as i~ is incidental, may be compared with the profuse swea~1n? from an agony of pain or terror. Nevertheless, It IS remarkable how slight an excitement often suffices to cause the hair to become erect; as when two dogs pretend to fight together in play. W"_ e have, ~lso, se~n in a large number of animals, belongin~ to widely di~tinct classes, that the erection of the hau or feathers Is almost always accompanied by various voluntary moveInents- by threatening gestures, opening th~ mouth, uncovering the teeth, spreading out of the wings and tail by birds, and by the u ttei'ance of harsh so_uncls; and the purpose of these voluntary moveme"?-_ts IS unmistakable. Therefore it seems hardly credible that the co-ordinated erection of the dermal appendages, by which the animal is 1nade to appear larger and more terrible to its enemies or rivals, should be altogether an incidental and purposeless result of the disturbance of the sensorium. This seems almost as incredible as that the erection by the hedgehog of its spines, or of the quills by the porcupine, or of the ornamental plu1nes by many birds during their courtship, should all be purposeless actions. \f\T e here encounter a great difficulty. How can the contraction of the unstriped and involuntary arrectores pili have been co-ordinated with that of various voluntary muscles for the same special pu1·pose? If we could believe that the arrectores primordially had been voluntary muscles, and had since lost their stripes. and become involuntary, the case would be comparatively simple. I am not, however, aware that there is any CHAP. IV. lN ANil\[AL~ '. 10'· evidence in favour of this view; althouo-h the revers d transition would not have presented ~1y great diffic~ l~y, ~s the voluntary n1u cles ar in an uustripod conchtion In the einbryos of the higher animals, and in tb larvre of some crustae ans. l\foreover in the deeper layers of the skin of adult birds, the muscular network i::;, according t Leydig, 20 in a tran ·itional condition; the fibres exhibiting only indications of transverse striatiou. Another explanation seems possible. We may admit that originally the arrectores pili were slightly acted on in a direct manner, under the influence of rage and terror, by the disturbance of the nervous system ; as is undoubtedly the case with our so-called goose-skin bef~re a fever-fit. Animals have been 1·epeatedly excited by rage and terror during many generations; and consequently the direct effects of the disturbed nervous system on the dermal appendages will almost certainly have been increased through habit and through the tendency of nerve-force to pass readily along accustomed channels. We shall find this view of the force ?f h~bit strikingly confirmed in a future chapter, where 1t will be shown that the hair of the insane is affected in an extraordinary manner, owing to their repeated accesses of fury and terror. As soon as with animals the power of erection had thus been strengthened or increased, they must often have seen the hairs or feathers erected in rival and enraged males, and the bulk of their bodies thus increased. In this case it appears possible that they might have wished to make themselves appear larger and more terrible to their enemies, by voluntarily assuming a threatening attitude and uttering harsh cries ; such attitudes and --- ------ :!o 'Lchrbuch dcr IIistologie,' 1857, s. 82. |
