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 trunks, 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 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 
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 the Tabanidae, 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. 
Sinneswerk. Hft. 1, Taf. II. fig. 24 (Cicada), and 
L. Dufour, Recherch. sur les Hémiptéres, p. 259, 
Pl. XIX. fig. 801-803 (Pentatoma, Nepa and 
Cicada).* 
6 For the nervous system of the Diptera, see 
L. Dufour, Ann. d. Sc. Nat. 1844, p. 245. 
7 L. Dufour, Ibid. III. 1845, p. 64, Pl. I. 
fig. 12. 
8 Burmeister, Handb. d. Entomol. I. 307, Taf. 
XV. fig. 11 (Eristalis tenaz). 
9 Swammerdamm,Bib. d. Nat. p. 270, Taf. XLI. 
fig. 7 (Stratiomys). 
10 I have found the ventral cord of the larva of 
Oestrus bovis concentrated into a single large 
ganglion, situated at the extremity of the thorax. 
I think, therefore, that the description of the nervous 
system of the larva of Oestrus ovis given by J. 
L. Fischer (Observ. de Oestro ovino atque bovino. 
Diss. Lips. 1787, p. 32, or in Werneri, Vermium 
* [§ 330, note 5.] For the nervous system of 
Belostoma, with all its details, see Leidy, History 
and Anatomy of the h ‘ous Genus Bel ‘ 
in the Jour. Acad. Nat. Sc. Philad. I. 1847, p. 65, 
Pl. X. fig. 13. — Ep. 
+ [§ 330, note 11.) In the larva of Corethra 
intestin. exposit. contin. tertia. p. 28, Taf. TIL. fig. 
4), and according to which, two long ganglionic 
cords, connected by transversal anastomoses, ex- 
tend the whole length of the body,—is based on inex 
act observations. Inthe larvae of Piophilaand Eris- 
talis, several ventral ganglia fused together form a 
single abdominal cord ; see Swammerdamm, Bib. 
der Nat. p. 279, Taf. XLIII. fig. 7, and Burmeis- 
ter, Handb. loc. cit. Taf. XVI. fig. 10. 
l The larvae of Stratiomys have an abdominal 
cord composed of ten contiguous ganglia (Swam- 
merdamm, Bib. der Nat. p. 264, Taf. XL. fig. 5). 
With those of Culex, Chironomus, Simulia, and 
other Tipulidae, the ten ganglia are wide apart, 
and connected by double longitudinal commis- 
sures.f 
12 In the apodal larvae and the larvae-like fe- 
males of Xenos Rossii, I have found this nervous 
mass in the first segment of the body which corre- 
sponds to the cephalothorax. 
plumicomis, Leydig found the ventral cord com- 
posed of eleven, instead of ten ganglia ; see Anato- 
misches und Histologisches tib. d. Larve von Core+ 
thra plumicornis in Siebold and Kolliker’s 
Zeitsch. III. 1852, p. 438. — Ep. 
