THE EYES OF INSECTS. 195 



the peculiar satin-like lustre of the insect's eye. Their number 

 is almost incredible, for in the domestic fly there have 

 been reckoned 4,900, in the cockchafer 6,300, and in some 

 butterflies no less than 60,000 eyes, each receiving its separate 

 ray of light and transmitting the impression to the brain ! 



The use of this compound structure of the organs of vision is 

 evident, for had the eye of the insect been simple as ours, it 

 would have required a large number of muscles, occupying a 

 considerable space and adding greatly to the weight of the 

 head, to turn it in its socket, and a constant attention and 

 change of position to protect its owner from the manifold 

 dangers to which he is exposed ; while now, with its thousands 

 of eyes collected into two prominent and immoveable groups, and 

 economizing both space and labour, the insect without any effort 

 constantly commands a vast horizon. 



Who would not have imagined that instruments so prodigally 

 endowed would have sufficed for every purpose? but in many cases 

 two or three minute and simple eyes, situated on the forehead 

 or summit of the head, have been superadded to their number. 



The celebrated physiologist Professor Miiller is of opinion that 

 the function of these simple eyes is confined exclusively to the 

 perception of near objects, and that of the compound eyes to 

 more distant ones ; so that we thus find the sight of many insects 

 as capable of embracing every range of vision, as civilized man 

 with the artificial assistance of his near and farsighted spectacles. 



The simple eyes or ocelli constitute the only organs of vision 

 in the larva state, where the compound eye would clearly have 

 been superfluous ; as at this early stage of their development 

 insects are not obliged to seek their food at any great distance, 

 and, were they able to perceive an enemy from afar, have not the 

 power of escaping by a rapid flight. 



As the food of the different orders of insects is extremely 

 various, it may easily be imagined that their mouths must also 

 be very differently constructed. In those which bite, tear, or 

 lacerate, it is furnished with very strong jaws, often notched or 

 serrated on the inner side into the appearance of teeth, and 

 sometimes decussating like the blades of a pair of scissors ; in 

 others it consists of a tube or instrument for suction, either simple 

 or armed with various kinds of appendages. 



Thus in the Tabanidae it is furnished with sharp lancets, to 



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