4 THE INSECT WORLD. 



elliptical or conical eyes, which one generally finds among insects, 

 ^re \e^?, Dcrfect than those referred to above. 



"'" " Th^ dSerences which exist in the organisation of the eye 

 among insects are explicable, to a certam point, «" *« J^^^es 

 which we are about to explam '^ a few words Those species 

 which live in the same substances on which they feed and those 

 which are parasitical, have small and flattenea eyes; those on the 

 Tontary which ave to seek their food, and which need to see 

 SctsVa'distance, have large or f^X ---j^^- ,, ^3°^!'^: 

 <iame reason the males, which have to seek their females, nave 

 aT^er eyes than the latter. The position of the eyes depends also 

 onfheir size and shape; those which are flat, and have consequently 

 a short field of vision, are placed close together^ and ratherm front 

 Ln a the sides of he head, and often adjoining. Spherical and 

 convex eves on the contrary are placed on the sides and their 

 axes are opposUe. But the greater field of vision which they are 

 able to take in makes up for this position. ' 



Almost all insects Le provided with a pair of compound eyes 

 which are placed on the sides of the head. The size and form of 

 these organs are very variable, as we shall presently see. They are 

 senerallv placed behind the antenna. 



^ AUhough simple eyes (ocdli or stemmata) are common, they do 

 not txist in all the orders of insects. They are generally round and 

 Siore o less convex and black, and there are three in the majority of 

 ™ases When there is this number they are most frequently placed in 

 a tilange behind, and at a greater or less distance from the antenna. 

 UndTr he cornei, which varies in convexity, is found a transparent, 

 father ha^d, and 'nearly globular body, which is the tnie cry^ a Ime 

 resting on a mass, which represents the vitreous body. Th>^;'t',^°"^ 

 body is enclosed in an expansion of the optic nerve. Besides these, 

 there is a pigment, most frequently red-brown, sometimes black 

 or blood-red. The organisation of these eyes is analogous to the 

 eves of fishes, and their refractive power is very great. 

 ' With these eyes insects can only see such objects as are at a ,hoit 

 distance Of what use then can stemmata be to insects also provided 

 wUh compound eyes ? It has been remarked that most insects having 

 h s a'-Lgement of eyes feed on the pollen of plants, and .has been 

 surmised that the stemmata enable them to distinguish the parts of 



*^ The'lntenn^, commonly called horns, are two flexible appendages, 

 of very variable form, which are joined to different parts of the head 

 and are ^Jways two in number. The joints of which they are made 



