410 THE INSECTA. ^ 330. 



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

 ganglia pass off, in a ventral cord, two main tninks, approximated, which 

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

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



With the Diptera, 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 Ilippoboscidae,^'* the Oestridae, 

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

 glion, from which j)ass off nerves in various directions. The Muscidae 

 acalypterae, 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, Leptidae, 

 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, 

 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 quite wide apart ; 



5 Treviranus, Beitr. zur Anat. u. Physiol, d. iutestin. exposit. contin. tertia. p. 28, Taf. III. fig. 

 Sinneswerk. Hft. 1, Taf. II. fig. 24 (Cicada), and 4), and according to which, two long ganglionic 

 L. Dufour, Recherch. sur les Hemiptfires, p. 259, cords, connected by transversal anastomoses, e.x- 

 V\. XIX. fig. 801-S03 (Pentatoma, Ne.pa and tend the whole lengtli of the body, — is based on ine.\- 

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



6 For the nervous system of the Diptera, see talis, several ventral ganglia fused together fonn a 

 L. Dufour, Ann. d. Sc. Nat. 1844, p. 245. single abdominal cord ; see Swammerdnmm , Kib. 



^ L. Dufour, Ibid. III. 1845, p. 64, PI. II. der Nat. p. 279, Taf. XLIII. fig. 7, and Burmeis- 



flg. 12. ■ ter, Handb. loc. cit. Taf. XVI. fig. 10. 



>^ Bui iiieister, Handb. d. Kntomol. I. 307, Taf. U The larvae of Stratiomys have an abdominiil 



XV^I. fig. 11 {Eristalis tenax). coi-d composed of ten contiguous ganglia {Swam- 



i' 5u)ammerda»im,Bib. d.Nat. p. 270, Taf. XLI. merdamm. Bib. der Nat. p. 264, Taf. XL. tig. 5). 



fig. 7 (Stratiomys). With those of Culex, Chironomus, SimuUa. and 



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



Oestrus bovis concentrated into a single large and connected by double longitudinal comniis- 



ganglion, situated at the extremity of the thorax, sures.f 



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



system of the larva of Oestrus ovis given by J. males of Xenos Rossii, 1 have found this nervous 



L. Fischer (Ohserv. de Oestro ovino attiue bovino. mass in the first segment of the body which corre- 



Diss. Lips. 1787, p. 32, or in fVerneri, Vermium spouds to the cephalothorax. 



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

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

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

 in the Jour. Acad. Nat. Sc. Philad. I. 1847, p. 65, tlu-a phmiicornis, in Siebold and Kulliker''s 

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



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



