THE CHARACTERISTICS OF INSECTS. 



229 



The maxillary palpi include from one to six pieces or joints. 

 The labial palpi have from two to four. The intermediate piece, 

 or tongue, is subject to great modifications. With the chin, it 

 completes the buccal pieces. 



In the licking and sucking insects the organs we have de- 

 scribed are adapted to their new functions. Thus the tongue in 

 bees reaches a great development ; bugs, grasshoppers (Fig. 9), 

 and lice have a long beak enveloping silky hairs, which form 

 rudiments of jaws ; in the butterflies we perceive a dispropor- 



Fig. 9. 



Fig. 8. 



Fig. 8. Mouth of a Bee. 5, tongue ; c c, labial palpi ; d, mandibles ; e, jaws ; /*, inner 

 lobe ; o. upper lip, or labrutn. 



Fig. 9. Beak of a Grasshopper. 



Fig. 10. Trunk of a Bdtterflt. 



tionately long proboscis \ while in the Diplera the dispositions 

 vary with the different groups. But in all these transformations 

 the attentive observer will be able to perceive vestiges of the 

 pieces comprising the mouth of the masticating insect which 

 we have chosen as a type. These homologies were clearly estab- 

 lished by De Savigny in 1816. 



The eye and the head in vertebrates are movable. The visual 

 rays consequently embrace a large horizon. The eye of the insect, 

 on the contrary, is immovable, and solidly incased in the head ; 

 and the movements of the head itself are very limited. A great 

 inferiority would result from this, had not Nature compensated 

 for it by augmenting the circle of action of the eye itself. The in- 

 sect's eye is formed by the union into a single mass of a consider- 

 able number of little eyes sometimes exceeding twenty thousand 

 (Fig. 11). Each of these minute organs, which are easily distin- 

 guished with a glass, comprises a hexagonal facet, representing 

 the cornea ; below this, a conical refracting mass represents the 

 crystalline lens, and upon this abuts the nervous net emerging 

 from the ganglion, which is itself in relation with the cerebral 

 mass. The apparent part of the eyes is rounded, like a spherical 

 cap, or rather like a portion of an ellipsoid. Sometimes the inner 



