INSECT 



corn beetles, as a shield for the mouth. That there 

 are grounds for not strictly regarding it in every in- 

 sect as a mouth-shield, cannot be denied ; but it 



847 



Figs. 57, Head of Brentus ; 58, ditto Fulgora, 59, Apoderus; 

 60, Diopsis. 



would be equally incorrect to reject it on that 

 account, as it would be to reject that of labrum, or 

 upper lip, because the latter organ occasionally is 

 quite unserviceable as a lip. Still less do we feel 

 inclined to regard it as a nose. Its form is very 

 variable according to the form of the head. Thus, in 

 an elongated head, it will be distinct and square, or 

 rounded ; and in those with a shorter head it is 

 transverse. In the rose beetle it has a deep frontal 

 notch ; in the sacred beetle it is ornamented with 

 several scalloped notches ; in the hornet it is sub- 

 quadrate ; in the grasshopper rounded ; and in the 

 rove beetle transverse. 



The organs of sense affixed to the head are : 

 Fixed a The composite eyes. 



b The ocelli, or single eyes. 

 Moveable c The antennae. 



d The trophi, or organs of the mouth. 

 In relation to the mutual dependence of these 

 organs upon each other, and upon the general cha- 

 racter of the insect, we are sure that we cannot do 

 our readers greater service than by quoting the fol- 

 lowing admirable passage, by Mr. Newman, from the 

 Entomological Magazine : " Professor Rang has 

 prettily observed, that every instrument, whether it 

 be for the generation or transference of power, has a 

 best size and a best form. Nature, in the formation 

 of her instruments, has always adopted that best size 

 and best form. If her creatures wanted but to see, a 

 globular eye floating in space might perhaps be the 

 uniform character of the animal world ; if to see and 

 to eat, an eye and a mouth would be given ; if to 

 move swiftly in the air were desirable, wings must be 

 supplied ; if on earth, legs must be added ; if in the 

 water, fins. To carry all these organs, and to contain 

 muscle to guide and govern them, a body must be 

 added. Each part of the body will be of the best 

 size and best form for the functions it has to perform. 

 We have seen that insects in their larva state have a 

 very uniform allowance of muscle to each segment. 

 In the imago the charge of supporting the whole body 

 in the air is entrusted sometimes to a single segment; 

 and, in order to supply sufficient strength for the 

 purpose, nature robs the neighbouring segments of 

 their muscle, and gives it the one which needs it. 

 In the head, the mouth-feelers and eyes operate in the 

 same manner one on another. Observe the dragon- 

 fly, the emperor of his tribe ; his wings rustle as he 

 hovers stationary and hawk-like in the air ; his appetite 

 is insatiable ; his food the active occupants of his own 

 element ; it is given to him in charge to set bounds 

 to the increase of the insect race ; he beholds his 

 prey afar off; he darts on it like the rapidity of a 



lightning flash ; to devour it ere life is departed is 

 the work of an instant ; he sails round and round ; 

 he soars up and down ; when the sky is serene, he 

 seeks his prey, like the swallows, almost beyond the 

 reach of human sight. What organs does such an 

 animal require ? Are they not these, eyes, mouth, 

 and wings? How has nature provided for his wants? 

 Regard his head below, it is all mouth ; above, it is 

 one continuous eye. Contemplate his wings their 

 character is strength and lightness, power and acti- 

 vity. His body is slender and graceful ; like a rud- 

 der, it serves as an instrument wherewith to shape his 

 course. Porrected feelers, whether cranial, lateral, 

 or maxillary, would be comparatively useless to an 

 animal whose dependence for support is on the keen- 

 ness of its vision and the velocity of its flight. We 

 find them but little prominent ; his every organ of the 

 required size. The same law obtains as certainly 

 and unvaryingly in form. There is truly a best form 

 and a best size, and Nature always provides both." 



a. The composite eyes. The eyes of insects, unlike 

 those of the higher animals, are immovable, horny, 

 and unprotected by any eyelid, of a large size, and 

 placed at the sides of the head, sometimes entirely 

 occupying the sides, and sometimes being so exten- 

 sive that scarcely any other part of the head is left 

 perceivable ; moreover, it is a curious circumstance, 

 that the eyes are sometimes clothed on the outer 

 surface with fine bristles. These organs are gene- 

 rally hemispheric, and of a circular, oval, or kidney- 

 shaped form ; and when more closely examined, they 



6Z 



Figs. 61, Head and eyes of the bee ; 62, Part of the facetted por- 

 tion showing the hairs between the facets. 



are found to consist of a very great number of minute 

 hexagonal lenses, giving the eye a reticulated appear- 

 ance. Each of these lenses operates as a distinct 

 organ of vision, and hence the number of the eyes 

 may be said to correspond with the exact number of 

 these hexagonal facets ; various calculations have 

 been made as to the number of these organs. Muller 

 has given a list of their number as derived from the 

 observations of Swammerdam, Leuwenhoeck, Andre, 

 Baster, Reaumur, Lyonnet, Goetze, Puget, and 



Schelver. 



Lenses. 



In the ant there are ... 50 

 In the convolvulus sphinx . . . 1300 

 In the common house fly . . 4000 

 In the silk-worm moth . . . 6236 

 In the goat-moth . . . .11300 

 In tho dragon-fly . . . 12544 



In a butterfly .... 17356 



In a mordella 25088 



And, according to a calculation cited by Geoffrey, 

 there must be not less than 34,650 of such facets in 

 the eye of a butterfly. W T hen one of the eyes is de- 



