§$ 887. THE INSECTA. 419 
ganglion on the extremity of the optic nerve, a short distance from the 
brain.“ ach lens-like pyramid with its vitreous body and nervous fila- 
ment is enveloped by a Chorioidea usually of a brown color, which forms, 
behind the cornea, a kind of pupil,“ but to which are due, by no means, 
the beautiful colors so often observed in the eyes of these animals. 
The size and form of the compound eyes, as also the number of their 
facets, are very varied.“ The larvae and pupae of the hemimetabolic 
Insecta have, usually, a less number of facets and consequently smaller 
eyes, than the perfect forms. With the Libellulidae, and Diptera, the eyes 
are very large ;“? while with the Formicidae, they are perhaps the smallest 
of all. With many Diptera, and some Hymenoptera, those of the males 
are much larger than those of the females, and are often contiguous in 
front or above.“® With some Hymenoptera, and Diptera, they are 
pilose, — the hairs being inserted in the angles of the facets. 
The compound eyes are usually spherical or oblong; and, with many 
Cerambycidae, and with the Vespidae, they are deeply emarginate in front, 
or on their internal border. With Diopsis,™ they have a very singular 
appearance, being supported on two very long, rigid, frontal processes, and 
their direction cannot, as with other Insecta, be changed without a turning 
of the head.©» 
CHAPTER V. 
DIGESTIVE APPARATUS. 
§ 337. 
The Insecta very often use their labial and maxillary palpi to seize and 
to convey food to the mouth, and even to introduce it wholly within this 
jast. With many species, the fore-legs are used to seize and retain the 
food, and the first pair is sometimes changed for this purpose even into 
rapacious organs.” With the larvae and pupae of the Libellulidae, there 
18 According to Miller (Arch. 1835, p. 613), 
these retinae are formed only by a prolongation of 
the neurilemma, while the proper nervous sub- 
stance does not extend beyond the extremity of the 
vitreous body; but Wild denies this (Miller's 
Arch. 1843, p. 349). 
14 Each of these pupils, according to Will (Miul- 
der’s Arch. 1843, p. 350), is moved by thirty to 
thirty-five delicate fibres which arise on the four 
transparent cylinders surrounding the pyramidal 
denses ; but Brants (Tijdsk. voor natuurhjke ge- 
schied. en physiologie. 1844, EI.) regards them as 
trachean branches and not contractile fibres. 
15 The beautiful emerald color of the eyes of 
anany Libellulidae, Tabanidae, Hemerobidae, &c., is 
due to the corneae ; for the chorioideae are of the 
‘same dead color as those of other Insecta. 
16 There are ti several thc ds of 
these facets in the eyes of large size; see Muller, 
Zur vergleich. Physiol. d. Gesichtssinn, &c., p. 340 ; 
and Wiil, Beitrag. &c. p. 10. 
17 The largest eyes are observed with the Heno- 
pidae, where they cover nearly the whole head ; 
see Erichson, Entomographien. Hft.I. p.132, Taf. I. 
18 Among the Hymenoptera, the genera Astata, 
Larra, Tachytes, Apis ; and among the Diptera, 
the Muscidae, Syrphidae, Leptidae, Tabanidae, 
Stratiomydae, and many other families. 
19 With Apis, Tabanus, Anthomyia, Eristalis, 
Volucella, and other Diptera. 
2 See Linné, Amoenitates academicae. VIII. 
Tab. VI. and Datman, in Fuessly’s Archiv’ d. 
Insekt. Hft. 1, Taf. VI. or Isis, 1820, p. 501, Taf. V. 
21 The Insecta scarcely move their head when 
they look in different directions. This renders very 
singular the extended mobility of the head with 
Mantis relizgiosa, which, in watching for its prey, 
looks on all sides. 
1 For example, with Syrtis, Naucoris, Nepa, 
Ranatra, Hemerodromia, Mantis, Mantispa, 
&e. 
