en. IV.] SUBSTITUTION OF NERVE-ACTIONS. 285 



the external impressions shall be applied in such order, and 



with such energy, that in a like order and with proportionate 



vigour, those voluntary movements are excited, which we con- 



jsider as the sentient actions of the instincts (265), remembering 



the same time how closely these are related to the ordinary 



lerve-actions caused by these impressions, it can hardly be a 



latter of surprise, that the latter take place as regularly and 



adaptively, as if they were sentient actions. Our astonish- 



lent, as we have already shown, arises from our erroneous 



►Delusions (438). Is not that which appears to be performed 



laptively, volitionally, and in a definite order, by a worm 



dthout a head or brain, by an insect, or by any other animal 



^hose structure is widely different from that of sentient beings, 



Ithough in such we can scarcely trace vegetative life — is not 



the whole life of an oyster, a sea-worm, a polype, a snail, 



spider, a flea, an ant, a bee, &c. — is not the whole of their 



lets, or part of them, solely an operation of the vis nervosa ? 



[ay, are they not such even in sentient animals ? We know 



)f no reason why it should be doubted, that such is the case 



dth those animals whose organisms are not constructed to be 



le seat of mind, like the bodies of sentient animals, but are 



lanifestly so formed as to lead to the conclusion, that the 



lervous ganglia, so numerous in many, perform the office of 



brain, and that the external impressions which nature sup- 



)lies, are so reflected from them to the limbs, that the latter 



ire excited thereby to perform those movements, according to 



the pre-ordained intent of nature, which, in sentient animals, 



khe material ideas of the instinct develop in like manner by 



leans of the cerebral force. 



558. The external impressions, which cause the sensation of 



[weariness, lassitude, and fatigue, whence the instinct for repose 



ind sleep arises, develop the sentient actions of this instinct, as 



[nerve-actions ; namely, a relaxation in the activity of the cerebral 



forces, and the weakening of their action on the mechanical 



lachines (287, i), without the instinct itself being excited, and 



dthout being felt. A sudden pressure on the brain arrests 



[in a moment the operation of the cerebral forces, without the 



^nstinct for sleep being previously developed, and all conceptions 



[and sentient actions suddenly cease. Opium, when taken, 



texcites this instinct, and not only changes the vital movements 



