500 EXTERNAL ANATOMY OF INSECTS. 



certainly do not exist a . Whence we may conclude, as 

 was before observed b , that the faculty of emitting light 

 is rather given it as a means of defence than to guide it 

 in its path. 



The situation of compound eyes differs in different 

 tribes. In some, as in the Staphylinida, they are planted 

 laterally in the anterior part of the head ; in others, the 

 Carabi &c, in the middle ; in others again, Locusta 

 Leach &c, in the posterior part. In some, their station 

 is more in the upper surface, either before or behind ; so 

 that a very narrow space separates them, or perhaps none 

 at all. Instances of this position of the eyes occur in a 

 minute weevil (Ramphus Clairv. c ), and many Diptera, 

 &c. Of those that form an union on the top of the head, 

 some are placed obliquely, so as to leave a diverging 

 space below them, as in many Libellulina d , the drone c , 

 &c. Others, as Atractocerus, in which the eyes occupy 

 nearly the whole head, and unite anteriorly, have this 

 diverging space above their conflux. In Rhina barbiro- 

 stris Latr., another kind of weevil, they are confluent 

 below the head, at the base of the rostrum, and a very 

 narrow interval separates them above. In a large num- 

 ber of the Heteromerous beetles, they are set transversely, 

 in the Capricorn ones longitudinally. Their surface, 

 when they are lateral, has usually two aspects, oneprone 

 to see below, the other supine to see above. In general 

 the eyes are situated behind the antennae, so that their 

 position, whether it shall be anterior or posterior, de- 

 pends upon that of those organs. Often, indeed, as in 



» De Geer vii. 562. i> Vol. II. p. 228. 



c Ent. Helvet. i. t. xii. «' Plate VI. Fig. 10. 



t Kirby Mon. Ap. Angl. i. t. xi. Apis. **. e. 1./. 2. 



