INTERNAL ANATOMY OF INSECTS. 9 
larva of a saw-fly in which this part is formed of four 
nearly equal spherical bulbs a : in the Scorpion (to judge 
by the figure of Treviranus b ) the two lobes represent 
an equilateral triangle, the exterior angle of which ter- 
minates in several lesser spherical bulbs ; in Acrida viri- 
dissima, Nepa cinerea, Clubiona atrox, and the common 
Louse, the lobes are pear-shaped c . 
ii. Tlic spinal marrow arid its ganglions d . From the 
posterior part of the brain of insects, but in the ground 
and water beetles (Eutrech'ma and Eunechma) from its 
sides below e , issue two chords which diverging embrace 
the oesophagus, and dipping below it and the intestines, 
— a situation they maintain to the end of their course, — 
and in their further progress uniting at intervals and 
dilating into several knots or ganglions, compose their 
spinal marrow. This part is so named, from a supposed 
analogy to the spinal marrow of vertebrate animals, 
which however admits of some degree of doubt ; yet, 
since it mixes the functions of that organ with those of 
the great sympathetic nerves, the denomination is not 
wholly improper, and may be retained. Though this 
chord is usually double when it first proceeds from the 
brain, and surrounds the oesophagus like a collar, yet in 
some insects it may be called a single chprd. This is 
the case with that of the common louse, in which Swam- 
merdam could perceive no opening for the transmission 
of the part just named f ; if he was not mistaken in this, 
the brain, as well as the rest of the spinal marrow in 
a Cuv. Anat. Comp. 324. b Arachnid, t. \.f. 13. m.m. 
c Cuv. ubi supr. 343. 346. Treviranus Arachnid, t. v. /. 45. a, 
Plate XXI. Fie. 8. a. 
" Ibid. Fig. 1 . b.b. ' Cuv. ubi supr. 33/. 
' Plate XXI. Fig. 8. Swamm. Bibl. Nat. i. 36. b. 
