418 



THE INSECTA. 



$336. 



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 [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 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 hesopod 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 



lula, see Treviranus, Beitr. &c. p. 84, Taf. II. 

 fig. 25-35. 



5 Bombus, Apis, Fespa ; see Treviranus, Bi 

 ologie, V. Taf. II., and his Beitr. &c. Taf. II. tig. 29 ; 

 and Brandt and Ratzeburg Medizin. Zool. II. Taf. 

 X.XV.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, Traite. &c. 

 p. 581, PI. XVIII. fig. 1, No. l,and fig. 6 (larva of 

 the goat-moth) ; Suckow, Anat. physiol. Unter- 

 such, p. 41, Taf. III. fig. 34 (pine caterpiHar), and 

 Burmeister, Trans. Entom. Soc. I. p. 239, PI. 

 X.XIII. fig. 7 (larva of a Calosoma). The three 

 stemmata of Cicada receive tlitir nerves from a 

 common trunk arising from tlie middle of tlie brain; 

 see Trevframis, Beitr. Taf. II. fig. 24, and L. 

 Dufour, Kecherch. sur les llemipt«5res, &c., PI. 

 XIX. fig. 203. 



7 See Nicotet, Recherch. sur les Podurelles, loc. 

 cit. p. 28, PI. II. III. 



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 oidy 

 two large stemmata on each side of the head, and 

 those of Lycus, MeLoe, Lampyris and Cantharis, 

 fiave only one. 



'•> See Templeton, Trans. Entom. Soc. III. p. 54, 

 Pi. IV. 



10 There are three front.'il stemmata with many 

 «f the Orthojitera (Mantidae, Acrididae, Liljelluli- 



dae, Perlidae, Psocidae, Ephemeridae and some 

 Pliasmidae) ; with some Neuroptera(//e7«ero/)iUÄ, 

 Panorpa, Phrys;anea), and Heiniptera (Penta- 

 toina, Coreus, Berytus, Cicada). This is the case 

 also with many Diptera, such as the Muscidae, 

 Syrphidae, Stomo.xidae, Bombylidae, Anthracidae, 

 Oestridae, Asilidae, Empidae, &o.; they are want- 

 ing with Talianus, Hae.matopota, Coyiops, Hip- 

 pobosca, Melnphnsus, and many of the Tipuhdae. 

 With the llynifii'i|)trra, they are constantly pres- 

 ent except witli tlir ni'uter ants and with the fe- 

 males of Mut Ma Mid Myrmosa; there are only 

 two of these eyes with most of (iryllus ; 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 Omaliu/n and 

 Anthophasus, of tlie Coleoptera. 



11 For the intimate structure of the compound 

 eyes, see Straus ((Jonsid. ä:c. p. 411, PI. I.V.), 

 iJugis (Ann d. Sc. Nat. X.V. 1830, p. 341, PI. 

 XII., or in Froriep\i Not. .\.\IX. p. 257), R. 

 Wagner {Wieg>naiin\s: Archiv, IS35, I. p. 372, 

 Taf. v.), and e.si)ecially fVil/ (Beitrug, zur Anat. d. 

 zusammengesezten Augen mit facettirt. Hornhaut. 

 1840). ' 



l'.i These differences in the size of the facets had 

 been o!)served by Marcel de Serres (loc. cit. p. 45) 

 with Lihellala. They e.xist also in the eyes of 

 Lngriaflava, gibbosa, alra, Tahnnus rusticus, 

 and some other Diptera; see Js/(<oa!, Trans. Eu- 

 tom. Soc. II. p. 253, PI. XXI. 



