$ 3386. 
418 THE INSECTA. 
on the brain that their optic nerves consist only of small papillae on this 
last ;© but, when further removed from the brain and grouped together, 
the optic nerves arise by a common trunk which divides into as many 
branches as there are eyes.® 
The number and disposition of the stemmata vary very much in the 
different orders. When they alone constitute the visual organs, they are 
always situated on the lateral parts of the head, where they may be 
disposed either, as one on each side, or as several irregularly grouped 
together (Ocellz gregati), or regularly arranged in rows (Ocelli seriati). 
There is only one simple eye on each side with the Pediculidae, Nirmidae, 
Coccidae, the larvae of the Phryganidae and Tenthredinidae, and the aquatic 
ones of very many Diptera. These organs are in groups of four to eight 
with the Poduridae,” with the larvae of Lepidoptera, the hexopod larvae 
of the Strepsiptera, the larvae of the Hemerobidae, Mymeleonidae, Raphi- 
didae, and with the hexapod ones of the Coleoptera.© The winged males of 
the Strepsiptera have the largest number of stemmata aggregated in groups ; 
they here form two lateral, globe-like projections, ‘and constitute the transi- 
tionary form to the faceted eyes, for there are fifty to seventy on each side, 
separated from each other only by hairs.© Very many Insecta with two, 
faceted eyes, have, also, on their front, three stemmata disposed in a 
triangle. 
2. The Compound eyes, or those whereof the cornea is faceted, are com- 
posed of simple eyes so thickly set together that their more or less thick, 
slightly convex, quadrangular, or hexagonal corneae are contiguous.” 
The size of these ‘facets is not uniform even in the same eye, for some- 
times those above, or those in the centre, are the larger.“? Behind each 
cornea is situated, in place of a lens, a transparent pyramid the apex of 
which is directed inwards and received into a, kind of transparent calyx 
corresponding to a Corpus vitreum. This last is surrounded by another 
calyx formed by the expansion of a nervous filament arising from the 
dula, see 
fig. 25+35. 
5 Bombus, Apis, Vespa; see Treviranus, Bi 
ologie, V. Taf. II., and his Beitr. &c. Taf. II. fig. 29 ; 
and Brandé and Ratzeburg Medizin. Zool. II. Taf. 
XXV. fig. 31, 32. 
6 With many of the larvae of the Lepidoptera 
. and the Coleoptera, the optic nerves arise by two 
more or less long roots; see Lyonet, Traité. &c. 
p. 581, Pl. XVIII. fig. 1, No. 1, and fig. 6 (larva of 
the goat-moth); Suckow, Anat. physiol. Unter- 
such. p. 41, Taf. III. fig. 34 (pine caterpillar), and 
Burmeister, Trans. Entom. Soc. I. p, 239, Pl 
XXIII. fig. 7 (larva of a Calosoma). The three 
stemmata of Cicada receive their nerves from a 
common trunk arising from the middle of the brain; 
see T'reviranus, Beitr. Taf. II. fig. 24, and LZ. 
Dufour, Recherch. sur les Hémipteres, &c., Pl. 
XIX. fig. 203. 
7 See Nicolet, Recherch. sur les Podurelles, loc. 
cit. p. 28, Pl. IL. IIT. 
8 Such are the carnivorous larvae of the Cara- 
‘bidae, Staphylinidae, Dytiscidae, Dermestidae, Sil- 
phidae, &c., and the herbiferous larvae of the 
Chrysomelidae. Those of Cicindela have only 
two large stemmata on each side of the head, and 
those of Lycus, Meloé, Lampyris and Cantharis, 
have only one. 
Pi 9 See Templeton, Trans. Entom. Soc. IIT. p. 54, 
1. IV 
Treviranus, Beitr. &c. p. 84, Taf. IT. 
10 There are three frontal stemmata with many 
ef the Orthoptera (Mantidae, Acrididae, Libelluli- 
dae, Perlidae, Psocidae, Ephemeridae and some 
Phasmidae) ; with some N europtera (Hemerobius, 
Panorpa, Phryganea), and Hemiptera (Penta- 
toma, Coreus, Berytus, Cicada). This is the’case 
also with many Diptera, such as the Muscidae, 
Syrphidae, Stomoxidae, Bombylidac, Anthracidae, 
Oestridae, Asilidae, Empidae, &c.; they are want- 
ing with Tabanus, Haematopota, Conops, Hip- 
pobosca, Melophagus, and many of the Tipulidae. 
With the Hymenoptera, they are constantly pres- 
ent except with the neuter ants and with the fe- 
males of Mutiila and Myrmosa; there are only 
two of these eyes with most of Gryllus ; Sciophila, 
Mycetobia and Leja, of the Diptera ; Sesia, Eu- 
prepia, Pyralis and a great number of the Noctu- 
idae, of the Lepidoptera ; Gryllotalpa, Blatta and 
Termes, of the Orthoptera; and Omalium and 
Anthophagus, of the Coleoptera. 
11 For the intimate structure of the compound 
eyes, see Straus (Consid. &c. p. 411, Pl. IX.), 
Duges (Ann d. Sc. Nat. XX. 1830, p. 341, Pl. 
XIL., or in Froriep’s Not. XXIX. p. 257), R. 
Wagner (Wiegmann’s Archiv, 1835, I. p. 372, 
Taf. V.), and especially Will (Beitrag. zur Anat. d. 
Tr ana Augen mit facettirt. Hornhaut, 
0). 
12 These differences in the size of the facets had 
been observed by Marcel de Serres (loc. cit. p. 45) 
with Libellula. They exist also in the eyes of 
Lagria flava, gibbosa, atra, Tabanus rusticus, 
and some other Diptera; see Ashton, Trans. En- 
tom. Soc. II. p, 253, PL XXI. 
