Insect Vision and Insect Sleep. 107 



we see the same object in another perspective; yet if we open both eyes 

 we do not see two images of the same object in different perspectives, 

 but only one object in proper visual union by coincident perception. 



" The moveable eyes in ourselves, and the immoveable eyes in 

 the insect, do not affect this analogy. The multitude of facettes 

 accommodate the immoveable eyes to a whole panorama. The 

 stereoscope will illustrate all the facts in both circumstances of 

 vision. In the stereoscope we have exhibited to us two representa- 

 tions of the same object in different perspectives : — the difference 

 corresponds with the distance between the two lenses through which 

 we are looking ; they are both immoveable, but visually combined 

 they are but one perception of one and the same object. In the 

 same way insects, with their multiplied incidents of vision, see by 

 coincidence but one representation from a multitude of eyes. 



" I trust, my dear sir, I have met your purpose in testing Puget's 

 experiment. 



" Believe me, etc., " Thus. D. Toase." 



II.— THE SLEEP OF INSECTS. 



The ocelli, or secondary eyes of insects, which Linneeus 

 regarded as a kind of coronet, and called stemmata, and which 

 Reaumur conceived were designed for that near vision, which 

 the primary eyes, by their immoveable structure, could not 

 accomplish with proper distinctness, have, I have but little 

 doubt, by the experiments which have been made on vision, 

 and on the excitement of sleep, a very important influence in 

 determining somnolency in insects. The vast field of objects 

 commanded in vision, without the concentration of attention, 

 is one of variety, but not of accuracy. In insects there is no 

 dilation or contraction of a pupil to accommodate the sight to 

 the circumstances of light and darkness. By attention we are 

 conscious of perception. If the attention be limited to one 

 point of a landscape, it sees only the objects there, and though 

 there be visual impressions, there are no visual perceptions, 

 where the mind is not attentively absorbed on what it is looking 

 at. It is without the consciousness of seeing. 



How do insects, with their great orbicular eyes always ex- 

 posed to external stimulants, sleep ? Sleep, like the inclination 

 for food, is periodical. The habit in the lower animals is the 

 alternation of light and darkness, in the degree in which one 

 indicates day and the other night, for in a total eclipse birds 

 retire to roost, and the diurnal insects resort to repose, and the 

 nocturnal awake.* The influence that tends to wakefulness or 



* Sir Hugh Lyon Playfair, in his lectures on the application of physiology to 

 the rearing of cattle (Lect. 2nd), gives a very remarkable illustration of the influ- 

 ence of rapid alternations of light and darkness, without reference to the diurnal 

 revolutions of the earth, in inducing sleep and inclination for food, in the Italian 

 mode of rapidly fattening ortolans. At a certain hour in the morning, the keeper 



