EXTERNAL ANATOMY OF INSECTS. 507 



micida, and the Reduviada very remarkably ; but many 

 others in both sections of this order, as Thrips, Coccus, 

 Aphis, Capsus, Miris, Naucoris, Nepa, and Notonecta, &c. 

 are deprived of them a . Of the Neuroptera the Libellu- 

 lina add stemmata to their large eyes, in the anterior 

 angle of which they are stationed 5 ; but many other ge- 

 nera of that Order are without them ; as Myrmeleon, As- 

 calaphus, Hemerobius, &c. The Trichoptera and Lepi- 

 doptera universally have them ; though in the latter, 

 except in Castnia and the Sphingidce, they are not ea- 

 sily seen. In the Hymenoptera they are usually very 

 conspicuous, but in Larra and Lyrops, two genera of this 

 order, the posterior pair are scarcely discernible ; and in 

 the neuter ants they are quite obsolete. In the T>iptera, 

 though many genera are furnished with them, yet many 

 also want them ; amongst the rest Latreille's Tipularice, 

 and all the horse-flies (Tabanus L.). The Pupiparte 

 {Hippobosca L.) usually have none; but in Ornithomyia 

 avicularia, one of that tribe, though extremely minute 

 they are visible, arranged in a triangle, in the polished 

 space of their vertex. 



As to the Number of the stemmata, three appears to 

 be most universal. Reaumur mentions an instance in 

 which he counted four in a fly with two threads at its 

 tail; but great doubt rests upon this statement c . Some 

 Orthopterous genera, as Gryllotalpa, and many Hemi- 



a Flata phalcenoides F. and affinities have no stemmata, while 

 Flata reticulata and affinities have them : a proof that these tribes 

 are distinct genera. 



b Plate VI. Fig. 10. i. 



c Reaum. iv. 243. He refers for this insect to plate xiv. without 

 adding any number for the figure ; but no such is in that plate. 



