INTERNAL ANATOMY OF INSECTS. 17 



are sometimes interwoven with the muscles, as the woof 

 with the warp in a piece of cloth a ; those from the three 

 or four first commonly rendering to the muscles of the 

 legs, wings, and other parts of the trmi/c, and those from 

 the remainder to the abdomen. After their origin they 

 often divide and subdivide, and terminate in numerous 

 ramifications that connect every part of the body with 

 the sensorium commune. A pair of nerves is the most 

 usual number that proceeds from each side of a gan- 

 glion b ; but this is by no means constant, since in the 

 louse, the hive-bee, and several other insects, only a single 

 nerve thus proceeds c ; and in the larva of Ephemera, 

 while two pairs issue from the six Jirst ganglions, only a 

 single one is emitted by the jive last d . In the spinal mar- 

 row of the rhinoceros-beetle, both larva and imago, the 

 nerves consist of simple filaments which diverge like rays 

 in all directions c : the same circumstance distinguishes the 

 cheese-maggot, only some of the nerves appear to branch 

 at the end f : in the louse, the last ganglion sends forth 

 posteriorly three pairs of nerves which render to the 

 abdomen g . Sometimes, though rarely, nerves originate 

 in the internodes of the spinal marrow. Cuvier indeed 

 has asserted that in invertebrate animals all the nerves 

 spring from the ganglions, and never immediately from 

 the spinal marrow ; but Swammerdam, in describing 

 those of the silk-worm, mentions and figures four pairs 

 as proceeding from the four anterior internodes, exclud- 



a Cuv. ubi supr. 349. b Lyonet Anat. t. ix. x. 



c PLATE XXI. FIG. 8. Swamm. Bibl. Nat. t. xxii./. 6. 

 d Ibid. t. xv. / 6. e PLATE XXI. FIG. 7. 



f Swamm. ubi supr. t. xliii./, 7. A, h. 

 f PLATE XXI. FIG. 8. 

 VOL. IV. C 



