108 Insect Vision and Insect Sleep. 



to slumber is the condition of the nervous system. If its func- 

 tional activity be protracted, the vision gives way under the 

 exhaustion of the nervous powers. If the action of the mind 

 be purely intellectual, if the feelings be not excited under that 

 action, the waste sensorially suffered is to be repaired by sleep, 

 and the sensation of slumber becomes uncontrollable. The 

 demand for sleep is the desire to have it ; and whether the ab- 

 sence of sensorial impressions results from the settling of the 

 mind to rest, or whether it be that darkness cuts off all stimu- 

 lation from light, or silence conduces to repose, sleep is induced 

 by the cessation of all visiial or emotional excitement. If the 

 mind be withdrawn from the consciousness of it own operations, 

 or if it be acted upon by a monotony that either wearies, atten- 

 tion, or distracting it, leaves the sensorial image without per- 

 ceptive impression, the result is slumber, or the nervous relaxa- 

 tion of sleep. 



" Tir'd Nature's sweet restorer, balmy sleep ! 

 He, like the world, his ready visit pays 

 Where fortune smiles ; — the wretched he forsakes." 



Young's Night Thoughts. 



When the mind divides itself between the thoughts and 

 the emotions, mental activity being unsuspended and the feel- 

 ings unappeased, the restlessness of anxiety becomes the in- 

 quietude of wakefulness; and though there be weariness of 

 both heart and soul, the balm of slumber may be desired, but 

 tired Nature remains ungratified by the restoration of sleep. 



Having- thus indicated the circumstances under which being's 



a < o 



slumber, that combine an intelligent nature with a sensational 

 one, let us examine hoiv insects sleep. 



When the senses are blunted to external impressions under 

 the lessened excitability of the mind, and our ideas, more con- 

 fused than vivid, are carried beyond ourselves in time and 

 place, we instinctively lie down to repose. All the creatures 

 organized with eyelids close the eyes against the influence of 

 light. The temperature of the body sinks, owing to diminished 

 nervous energy, and we seek with soft things to rest upon, 



of the birds places a lantern in the orifice of the wall, made for the special purpose 

 of darkening and illumining the room. The dim light thrown by the lantern on 

 the floor of the apartment induces the ortolans to believe that the sun is about to 

 rise, and they wake and greedily consume the food upon the floor. The lantern 

 is withdrawn, and the succeeding darkness acting as an actual night, the ortolans 

 fall asleep. During sleep, little of the food being expended in the production of 

 force, most of it goes to the formation of flesh and fat. After the birds have been 

 allowed to repose for one or two hours to carry on digestion and assimilation, the 

 keeper again exhibits the lantern through the aperture. The mimic daylight 

 awakes the birds again ; again they rise and feed ; again darkness ensuc3, mid 

 again they sleep. The representative sunshine is made to shed its rays four or five 

 times every day, ami as many nights follows its transitory beams. The ortolans 

 thus treated become bike balls of fat in a few days. 



