THE VENTRAL, COUI). 279 



larvae of the Diptera, Hymenoptera, and Coleoplera. Among the 

 larvae of the Diplera I have found it in the rat-tailed maggot, and 

 have represented it in PI. XXXII. f. 3. It commences with two 

 branches, which spring from the large cerebral ganglion lying over the 

 oesophagus. These branches, which embrace the oesophagus, unite 

 beneath it into one flat, tolerably broad, nervous cord, which extends 

 to about the third pair of feet on the pectoral side, within the thoracic 

 cavity, and here obtusely terminates. On each side of this cord there 

 are from eight to nine small ganglia, whence the nervous filaments, as 

 also at the obtuse apex of the cord, radiate posteriorly. The last, pro- 

 ceeding from the end of the cord, are the thickest ; they extend down- 

 wards to the end of the abdominal cavity, and here distribute them- 

 selves with their terminal branches to the colon and the convoluted 

 tracheae lying at the end of the abdomen. 



We should doubtlessly find a similar structure of the nervous system 

 in the maggots of all the Diptera whose body is not divided into dis- 

 tinct segments. Upon the same principle, I think, I may conclude that 

 the fat and irregularly-jointed larvae of the Hymenoptera, namely, of 

 the bees and of the wasps, have a similar nervous system without 

 ganglia, and thence it would be explained how Swammerdam could 

 discover no nervous cord in the honey-bee *. In the larvae of Stra- 

 tiomys Chamceleon the nervous cord is likewise indeed considerably 

 shorter than the body, but it exhibits distinct ganglia, which, however, 

 follow immediately upon each other, and display no long connect- 

 ing cords, which we observe in the fly itself. According to Swam- 

 merdam's figure f , we find besides the cerebrum and cerebellum ten 

 consecutive and contiguous ganglia, and each sends off radiating lateral 

 nerves. 



Among the Coleoptera we perceive a similar nervous system without 

 ganglia among the larvae of the Lamellicornia. Swammerdam J and 

 Rosel observed it in the larva of the rhinoceros-beetle (Oryctes nasi- 

 cornis) ; in these also it is a very short ventral cord, which extends 

 as far as the proximity of the third pair of legs, and from the lateral 

 margins of which innumerable delicate nervous filaments proceed. In 

 this larva also the body is not separated into distinct segments and 

 joints, it exhibits rather irregular folds and constrictions, which are 



* Biblia Natura-, \>. 166. a. f Ibid. PI. XL. f. 5. 



Ibid. PI. XXVI11. f. 1. 



