EXTERNAL ANATOMY OF INSECTS. 499 



Leay (Lucanus fiebulosus K.) the eye appears also to be 

 divided in two by the canthus. In the Neuroptera Order 

 there is more than one instance of the same kind. In 

 Ascalaphus there are two considerable eyes on each side 

 of the head, which, though clearly distinct, meet like 

 those of many male flies and the drone. The male, like- 

 wise, of more than one species of Ephemera, besides the 

 common lateral eyes and the stemmata on the back of 

 the head, have a pair of compound eyes on the top of a 

 short columnar process a . In the Hemiptera Order, also, 

 an instance occurs of four eyes in the genus Aleyrodes b . 

 Amongst the vertebrate animals, there is an example of 

 eyes with two pupils in Anableps, a genus of fishes c , but 

 no vertebrate animal has four of these organs. That 

 many insects should have more than two eyes, will not 

 seem to you so extraordinary as that any should be found 

 that, like the Cyclops of old, have only one. There is, 

 however, an insect, before celebrated for its agility d 

 [Machilis polypodia Latr.), which has a single eye in its 

 forehead; or we may say, its eyes are confluent, without 

 any line of distinction between them except a small notch 

 behind. Now that I am treating of the number of eyes, 

 I must not forget to observe to you, that in some insects 

 no eyes at all have been discovered. In Polydesmus com- 

 planatus, on each side of the head there is an eye-shaped 

 portion separated by a suture, in which under a power- 

 ful lens I cannot satisfy myself that I can discern any 

 thing like the facets that usually distinguish compound 

 eyes. In Geophilus electricus, another myriapod, they 



* Plate XXYI. Fig. 39. b. 



b Latreille Gen. Crust, et Ins. iii. 73. c 2V. Diet. a" Hist. Nat. i. 479. 



* Vol. II. 320. 



2 K 2 



