§ 336. THE INSECTA. 417 



fore-legs directly below the coxo-tibial articulation/'' With a part of the 

 Locustidae/*' there is, on each side at this point, a fossa ; while with 

 another portion of this family,'" there are, at this same place, two more or 

 less spacious cavities (Auditive capsules) provided with orifices opening 

 forwards/^' These fossae and these cavities have each on their internal 

 surface, a long-oval tympanum. The principal trachean trunk of the leg 

 passes between the two tympanums, and dilates, at this point, into a vesicle 

 whose upper extremity is in connection with a ganglion of the auditory 

 nerve. This last arises from the first thoracic ganglion, and accompanies 

 the principal nerve of the leg. From this ganglion in question passes off a 

 band of nervous substance which stretches along the slightly excavated 

 anterior side of the trachean vesicle. Upon this band is situated a row 

 of transparent vesicles containing the same kind of cuneiform, staff-like 

 bodies, mentioned as occui-ring with the Acrididae. The two large tra- 

 chean trunks of the fore-legs open by two wide, infundibuliform orifices on 

 the posterior border of the prothorax, so that here, as with the Acrididae, 

 a part of this trachean apparatus may be compared to a Tuba Eustachii.^ 

 With the Achetidae, there is on the external side of the tibia of the fore- 

 legs, an orifice closed by a white, silvery membrane (Tympanum), behind 

 which is an auditory organ like that just described.*^ 



§ 336. 



The organs of Vision consist of simple, or of compound eyes.^' The 

 first occur chiefly with the larvae of holometabolic Insecta ; and the second 

 with Insecta in their perfect state. There are, however, many species 

 which have both kinds of eyes in their imago state. These organs are 

 wanting with only a few adult Insecta,'-' but are wholly absent with many 

 larvae and pupae of the holometabolic species.''^' 



1. The Simple eyes {Ocelli, Ste??i7nata) are composed of a convex, 

 spheroidal, or elliptical cornea, behind which is situated a spherical or 

 cylindrical lens, lodged in a kind of calyx formed by an expansion of the 

 optic nerve, and which is surrounded by a variously colored pigment-layer, 

 as by a Chorioidea.'^' These^ stemmata are sometimes so closely situated 



8 See my researches in Wiegmann's Arch. loc. 1 For the eyes of the Insecta, see Marcel de 



cit. p. 72, Taf. I. fig. 8-17. Sevres, Mem. sur les yeux comp. et les yeux lisses 



* Meconema, Barbitistes, Pkaneroptera, Pki/l- d. Ins. ; Treviranus, \eTm. Schrift. III. p. 147, 



loptera. and Beit, zur Anat. u. Physiol, d. Sinneswevka. 



•5 Decticus, Locusta, Xiphidium, Ephippi- Hft. I. p. 84 ; finally, J. Milller, Zur vergleich. 



fuera, Sa^a, Conocephalus, Callinemus, Acan- Physiol, des Gesichtssinn, p. 326, or in Ann. d. Sc. 



thodis, Pseudophyllus, &c. Nat. XVII. 1829, p. 242 (in extract), and his Me- 



B In his classification of the Locustidae, Bur- moir in MeckeVs Arch. 1829, p. 38. 



meister (Uandb. &c. II. p. 673) has made use of ^ The eyes are wanting in many species of Ptiti- 



the different forms of these orifices ; — differences, um. which live under the bark of trees (Erichson, 



however, which had before been pointed out by De- Naturgesch. d. Insekt. Deutschl. III. p. 32) ; with 



geer (Abhandl. Th. III. p. 285, Taf. XXXVII. fig. Anophthalmus, which live in caverns {Sturm, 



5 and 6) Lansdown Guilding (Linn. Trans. XV. Deutschl. Fauna Abth. V. Bd. XV.), and with Cla- 



1827. p. 153). viger, which live in ant-nests. 



7 These two infundibuliform orifices of the tra- 3 As such may be cited the larvae of Hymeno- 



cheae, which L. Dufour (Recherch. sur les Orthopt. ptera, excepting, however, those of the Tenthredini- 



&c. p. 279, PI. I. fig. 2) has called vessies airosta- dae ; those of the Diptera, which live in decompos- 



tiques, have generally been regarded as the stig- ing animal and vegetable substances ; those of the 



mata of the prothorax, although the true stigmata, Elateridae, Histeridae, Lamellicornes, Tenebrioni- 



of the ordinary form and size, are situated in front dae, and in general the apodal larvae of Coleo- 



of the orifices in question. ptera ; finally, the parasitic larvae of the Strepsi- 



S With Acheta achatina and italica, there is ptera, whose females are also blind in the imago 



a tympanum of the same size, on the internal sur- state. 



face of the legs in question ; but it is scarcely ob- 4 For the simple eyes of Dytiscus, see Miiller, 



servable with Acheta sylvestris, domestica and in Meckets Arch. \oc. cit. p. 39, Taf. III. fig. 1, 2 ; 



campestris for those of Cicada, Vespa, Bombus, and Libel- 



