4'J2 THE SENSORIAL FUNCTIONS. 



noticed in the higher orders of Annelida ; the 

 second, are the conglomerate eyes, which consist 

 of chisters or aggregations of simple eyes; the 

 third, are the compound eyes, which are formed of 

 a vnst assemblage of small tubes, each having its 

 respective apparatus of humours and of retina, and 

 terminating externally in a separate cornea, slightly 

 elevated above the general surface of the organ : 

 the fourth kind of eyes, which have not yet been 

 distinguished by any particular appellation, are 

 constituted by a number of separate lenses, and 

 subjacent retina?, but the whole covered by a single 

 cornea common to them all. 



Few insects are wholly destitute of visual organs, 

 either in their larva? or perfect states.* The larvae 

 of those insects which undergo a complete meta- 

 morphosis have only simple eyes ; but those which 

 are subjected only to a partial change of form, as 

 the Orthoptera, the Hemiptera, and the aquatic 

 Neuroptera, have compound as well as simple eyes. 

 Perfect insects, with the few exceptions above no- 

 ticed, have always compound eyes, generally two in 

 number, placed on the sides of the head ; and they 

 are often accompanied by stemmata situated be- 

 tween, or behind them, on the upper part of the 

 head. These stemmata, when met with, are gene- 

 rally three in number, and are either placed in a 



* This is the case, however, with the genera Claviger and Anom- 

 mata, among the Coleoptera; Braula (Nitzch) among- Diptera, and 

 also some of the species of Pupipura, Nijcteribia and Melophagus, 

 which are all parasitic insects : there are also several species of ants, 

 whose neuters have no eyes. (Muller, Annales des 3c. Nat. xvii. 

 366.) The insects composing the genus Typhlopone, which are 

 closely allied to the Ant, and of which Mr. Shuckard has described 

 four species, are destitute of eyes. 



