418 ' THE INSECTA. ^ 336. 



on the brain that their optic nerves consist only of small papillae on this 

 last ;<^ bnt, 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 thej' 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 [Ocelli 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 thePhryganidae andTenthredinidae, and the aquatic 

 ones of >very many Diptera. These organs are in groups of four to eight 

 with the Poduridae,''^* with the lai'vae of Lepidoptera, the hexopod larvae 

 of the Strepsiptera, the larvae of the Hemerobidae, Mymeleonidae, Raphi- 

 didae, and with the hesapod 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 



lula, see Treviranus, Beitr. &c. p. 84, Taf. n. dae, Perlidae, Psocidae, Epherheridae and some 



fig. 25-35. Phasmidae) ; w\th some Heuroptt'ra, (Hemerobius, 



B Bombus, Apis, f^espa ; see Treviranus, Bi Panorpa, Phryganea), and Xleiniptera (Penta- 



ologie, V. Taf. II., and his Beitr. &c. Taf. II. fig. 29 ; toma, Coreus, Berytus, Cicada). Tliis is the case 



and Brandt and Ratzeburg Medizin. Zool. II. Taf. also with many Diptera, sucli as the Muscidae, 



XXV. fig. 31,32. Syrphidae, Stomoxidae, IJombylidae, Anthracidae, 



<! With many of the larvae of the Lepidoptera Oestridae, Asilidae, Empidae, &c.; tliey arc want- 

 and tlie Coleoptera, the optic nerves arise by two ing with Tabanus, Haematopota, Conops, Hip- 

 mure or less long roots; see Lyonet, Tniiti. kc. pobosca, Melopliagus, a.ni\ many of the 'tiimlidae. 

 p. 5S1, PI. XVIII. fig. 1, No. l,and fig. 6 (larva of With the Hymenoptora, they are constantly pres- 

 the goat-moth) ; Suckow, Anat. physiol. Unler- ent except with the neuter ants and with the fe- 

 such. p. 41, Taf. III. fig. 34 (pine caterpillar), and males of Mutilla and Myrmosa ; there are only 

 Hurmeister, Trans. Eiitom. Soc. I. p. 239, PI. two of these eyes with most of Gri/Z/us ; 5cio;)/«7a, 

 XXIII. fig. 7 (larva of a Calosoma). The three Mycetobia and Leja, of the Diptera ; Sesia, Eu- 

 stemmata of Cicada receive their nerves from a ;;re;)?a, P)/rn/is and a groat number of the Noctu- 

 cummon trunk arising from the middle of the brain; idae, of the Lupidoptera ; Gryllotalpa, Blatta and 

 8ee Treviranus, Beitr. Taf. II. fig. 24, and L. Termes, of the Orthoptera ; and Omalium and 

 Duf'our, Recherch. sur le3 Hemiptdres, &c., PI. Anthophagus, of tlie Coleoptera. 

 XIX. fig. 203. II For the intimate structure of the compound 



7 See Ninotet, Recherch. sur les Podurelles, loc. eyes, see Straus (Consid. &c. p. 411, PI. IX.), 

 cit. p. 28, PI. II. III. Diigcs (Ann d. Sc. Nat. XX. 1830, p. 341, PI. 



8 Such are the carnivorous larvae of the Cara- XII., or in Froriep's Not. XXIX. p. 257), R. 

 bidae, Staphylinidae, Dytiscidae, Dermestidae, Sil- fVagner (JViegmanri's Archiv, 1835,1. p. 372, 

 phidae, &c., and the herbiferous larvae of the Taf. V.), and especially IVill (Beitrag. zur Anat. d. 

 Chrysomelidae. Those of Cicindela have only zusammengesezten Augen mit facettirt. Ilornhaut. 

 two large stemmata on each side of the head, and 1840). 



those of Lycus, Meloc,Lampyris and Cantkaris, 1-i These differences in the size of the facets had 



have only one. been observed by Marcel de Scrres (loc. cit. p. 45) 



9 See Templeton, Trans. Entom. Soc. III. p. 54, with Libellula. They exist also in the eyes of 

 PI. IV. Lagriajiava, gibbosa, atra, Tabanus rusticus, 



10 There are three frontal stemmata with many and some other Diptera; see ^sAZon, Trana. En- 

 of the Orthoptera (Maatidae, Acrididae, Libelluli- torn. Soc. II. p. 253, PI. XXI. 



