Insect Vision and Insect Sleep. 109 



warm things to cherish us with heat, and then we go to sleep. 

 The lower animals instinctively do what we do, though each 

 accommodates itself differently. The horse will sleep standing 

 in the warm shelter of the stable, though it lies down in the 

 pasture ; the bird reposes perching, but with its head buried 

 in the feathers of the wing ; the serpent coils itself in a circle, 

 or folds itself into the smallest possible space ; the fish screens 

 itself in the weeds, or buries itself in the sand or in the mud 

 of the stream ; the insect withdraws from the scenes of its ordi- 

 nary activity, and is in a state of somnolent rest, when it re- 

 mains motionless. As the insect has no eyelids, no external 

 closure of the eye gives evidence of sleep. 



As all the [physiological facts of sleep in the vertebrate 

 animal coincide with effects exhibited by the heart and brain, 

 and as insects have neither of these organic centres, then sleep 

 cannot be induced by any peculiar change, either in lessening 

 or quickening the flow of blood from one extremity to the other, 

 but must result solely from the quietude of the senses, and from 

 electrical incidents externally. Monsieur Cabanis, in his Rap- 

 ports du Physique et Moral, has observed in man that some 

 of the members and senses go to sleep sooner than others. He 

 assigns the soporific influence sensationally to fatigue. The 

 part first feels drowsy in which the flow of the blood is affected. 

 Among the senses, the eye is the first that goes to sleep ; after 

 it, the smell, taste, hearing, and touch become successively 

 drowsy. The touch is never entirely insensitive. The sight 

 is more difficult to awaken than the hearing ; a slight noise 

 will rouse a sleep-walker who had suffered light upon his un- 

 shut eyes without any apparent influence; but insects, if 

 affected at all internally, are very little affected in this way. 



The insect world are acutely acted upon by atmospheric 

 circumstances. Rain or cloudy weather operates upon them like 

 a continuance or recurrence of night. It is not the warmth or 

 the dryness of the air, its humid state or its coldness ; it is the 

 electrical condition that affects them. The constant alternations 

 of sleep and waking, in whatever way they may be induced 

 by repose or affected by functional activity, are regulated as 

 periodical recurrences by the electrical laws of the seasons, by 

 the reiteration of day and night, by the daily variations of the 

 barometer, and by the conditions that move the magnetic needle 

 from east to west at stated hours every day. Extreme weari- 

 ness will prevent sleep if fatigue is unaccompanied by power- 

 less attention and unsettled sensation. Let us see how these 

 known facts may serve to explain the sleep of insects. 



We shall comprehend some of the physiological incidents 

 of slumber by attending to the processes of mesmeric sleep, as 

 developed by Mr. James Braid in his work on Neurypnology, 



