EXTERNAL ANATOMY OF INSECTS. 509 



actly between the two, being placed in the frontal angle. 

 In Fulgora their station is between the eyes and antennas a . 

 They are most commonly sessile, and as it were set in 

 the head ; but in some, as Fulgora candelaria, they stand 

 on a footstalk. The stemmata are set in the side of a 

 frontal tubercle in that four-winged fly of threatening 

 aspect, Corydalis, which in its perfect state has mandi- 

 bles, but longer and more tremendous, like those that 

 distinguish the larva only of the kindred genus Hemero- 

 bius b . These organs differ little in shape, being usually 

 perfectly round and somewhat convex ,• but occasionally 

 they vary in this respect. In Fulgora serrata they are 

 oblong, with a longitudinal depression ; in F. Diadema 

 they are also umbilicated, but the umbilicus is circular ; 

 in Corydalis they are oval; in other insects they are 

 ovate; in some semicircular, and in a few triangular. 

 They vary much in size: in some of these animals being 

 so minute as to be scarcely visible, while in others, as 

 Corydalis, Dorylus, Vespa pallida F., Reduvius, &c. b , 

 they are as large as some compound eyes. They differ 

 also in colour, though often black : in Fulgora laternaria 

 they are of a beautiful yellow,- in F. candelaria they are 

 white; in many Hymenoptera they are crystalline, in 

 others red. : the fierce look of Reduvius personatus is ren- 

 dered more hateful by its stemmata having a pale iris 

 round a dark pupil c . 



Let us here stop and adore the goodness of a benefi- 

 cent Creator, who, though he has deprived these little 

 beings of the moveable eyes with which he has gifted the 



* Plate XXVI. Fig. 41. i. 



b De Geer iii. t. xxvii./. 1. Reaum. iii. t. xxxii./. 3, 9. 



c Plate XXVI. Fig. 40. i. 



