410 THE INSECTA. ^ 330. 



they are connected by two long commissures. From the posterior of these 

 ganglia pass off, in a ventral conl, two main trunks, approximated, which 

 send off, in their course, lateral branches towards the periphery; with 

 Pentatoma, these two main trunks are fused into onc.'''^ 



With the Di;)tcra, the ganglionic chain is always connected by simple 

 commissures. The number of ganglia varies with the families, and, usually, 

 is proportionate to the length of the segments of the body.^"* The ven- 

 tral cord is most concentrated with the Hippoboscidae,*"* the Oestridae, 

 and the Muscidae calypterae ; it consists of only a single thoracic gan- 

 glion, from which pass off nerves in various directions. The Muscidae- 

 acalypterac, on the contrary, the Syrphidae''*' and the Conopidae, have, 

 beside this thoracic ganglion, one or two ventral ganglia ; while the Sceno- 

 pinidae have five, and theTabanidae, Stratiomydae,*''^ Therevidae, Leptidac, 

 Asilidae, and Bombylidae, have six. Their number is still larger with the 

 Empidae, Culicidae, and Tipulidae ; — there being, in the first, three tho- 

 racic and five abdominal ganglia; and in the last two, three thoracic and six 

 abdominal ganglia. The larvae of the Diptera usually have one more pair of 

 ganglia than the adults. It is only in those species whose ventral cord is 

 fused into a single mass, that the same concentration is observed with the ■ 



larvae."^"** The larvae of the Diptera have either a moniliform ventral 

 cord, composed of ten approximated ganglia, or a chain of eleven of these 

 masses, connected by long commissures, which are often double.^"' 



With the Strepsiptera, alike in the three states of larva, pupa and 

 imago, the ventral cord consists only of a large thoracic ganglion, from 

 which pass off nerves in various directions. ^'^^ 



With the adult Lepidoptera, the ventral cord consists of seven ganglia, 4 



of which the first two are the largest and belong to the thorax. The con- " 



necting commissures are not double except between the thoracic ganglia ; 

 those of the others being more or less fused into a single cord. In the ;' 



Caterpillars, the ventral cord consists of eleven nearly equal ganglia ; the 

 two commissures between the first three of these, are q^uite wide apart ; 



5 Treviranus, Beitr. zur Anat. u. Physiol, d. intestin. exposit. contin. tertia. p. 2S, Taf. III. fifj. 



Siiineswerk. Hft. 1, Taf. II. flg. 24 (^Cicada), and 4), and accordiiiK to which, two long ganglionic 



Z,. Z>M/o«r, Keohercli. sur les lleraipt^res, p. 259, cords, connected oy transversal anastomoses, ex- 



I'l. XIX. tig. 801-803 (Pentatoma, Nepa and tend the whole length of the body, — is based on inex- 



Cicada).* act observations. In the larvae of PiojoAiVa and Eris- 



U For the nervous system of the Diptera, see ta/js, several ventral ganglia fused together form a 



L. Dufoiir^ Ann. d. Sc. Nat. 1844, p. 245. single abdominal cord ; see Swammerdamm, liili. 



r L. Uufour, Ibid. III. 1845, p. 64, PI. TL. der Nat. p. 279, Taf. XLIIl. fig. 7, and Burmeii- 



iirr. 12. ter, Handb. loc. cit. Taf. XVI. tig. 10. 



f* liui fiiciiter, Ilamlb. d. Entomol. I. 307, Taf. U The larvae of Stratiomt/s have an abd^miinal 



XVI. flg. 11 {Eristalis tenax). cord composed of ten contiguous ganglia {Swam- 



!» Sit)a7«merrfa7/im,Bib. d.Nat. p. 270, Taf. XLI. merdamm, Bib. der Nat. p.' 264, Taf. XL. lig. 5). 



fig. 7 (Slratiomys). With those of Ciilex, Chironomus, Siniulia. and 



10 I have found the ventral cord of the larva of other Tipulidae, the ten ganglia are wide apart, 



Ot.itrus bovis concentrated into a single large and connected by double longitudinal commis- 



gaiiglion, situated at the extremity of the thorax, surcs.t 



1 think, therefore, that the description of the nervous 1^ In the apodal larvae and the larvae-like fc- 



wystem of the larva of Oestrus ovis given by J. males of Xenos Rossii, I have found this nervous 



L. Fischer (Ol)serv. de Oestro ovino atque boviuo. mass in the first segment (jf the body wliich corre- 



Diss. Lips. 1787, p. 32, or in IVeraeri, Vermiura sponds to the cephalothorax. 



* [ § 330, note 5.] For the nervous system of plumicomis, Leydis:: found the ventral cord com- j. 

 Belostoma, with all its details, "see Leidy, History posed of eleven, instead of ten ganglia ; see Anato- 

 and Anatomy of the heraipterous Genus Belostoma, misches und Histologisches iib. d. Larve von Core- 

 in the Jour. Acad. Nat. Sc. Philad. I. 1847, p. 65, thra plimiicornis, in Siebold and KoUiker's 

 PI. X. fig. 13. — Ed. Zeitsch. HI. 1852, p. 4.38. — Ed. 



t [ § 330, note 11.] In the larva of Corethra 



