ZOOLOGY. 279 



i 



light received by one passes into another, and all the filaments being 

 severed from each other by the pigment, they in no way interfere with 

 one another. 



" We now see, by experiment, that as each ocellus takes up a dis- 

 tinct picture, each picture is, necessarily, slightly altered in perspective. 

 The images, by the direction of the facetted mirrors severally, are each 

 slightly varied ; but being united on the central ganglion, they form 

 one perception of one object, or one scene. This is only a multiplica- 

 tion of the incidents of our own vision with two eyes. If we close one eye, 

 we see an object in a certain perspective ; if we close that eye that was 

 open, and open that which was shut, 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 movable eyes in ourselves, and the immovable eyes in the 

 insect, do not affect this analogy. The multitude of facets accommo- 

 date the immovable eyes to a whole panorama. The stereoscope will 

 illustrate all the facts in both circumstances of vision. In the stereo- 

 scope we have exhibited to us two representations of the same object 

 in different perspectives : the difference corresponds with the dis- 

 tance between the two lenses through which we are looking ; they are 

 both immovable, but visually combined, they are but one perception 

 of one and the same object. In the same way insects, with their mul- 

 tiplied incidents of vision, see by coincidence but one representation 

 from a multitude of eyes." 



THE SLEEP OF INSECTS BY RICHAKD HILL. 



The ocelli, or secondary eyes of insects, which Linnaeus regarded as 

 a kind of coronet, and called ste?nmata, and which Reaumur conceived 

 were designed for that near vision, which the primary eyes, by their 

 immovable 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 influ- 

 ence 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 con- 

 traction 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 vis- 

 ual perceptions, where the mind is not attentively absorbed on what it 

 is looking at. It is without the consciousness of seeing. 



How tlo insects, with their great orbicular eyes always exposed to 

 external stimulants, sleep ? Sleep, like the inclination for food, is peri- 

 odical. 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. 1 The influence that tends to 



1 Lyon Playfair, in his lectures on the application of physiology to the rearing of 

 cattle, gives a very remarkable illustration of the influence of rapid alternations of 

 light and darkness, without reference to the diurnal revolutions of the earth, in in- 

 ducing sleep and inclination for food, in the Italian mode of rapidly fattening orto- 



