THE VENTRAL CORD. 281 



much-radiated terminal ganglion. We observe a nervous system com- 

 posed of thirteen ganglia not only in the caterpillars of the Lepidoptera, 

 but also in the larva of the Carabodea, the predacious beetles, the 

 majority of the Heteromera (Meloe, Lytta), the capricorns, and pro- 

 bably also in the Chrysomela ; in the fat footless larvae of the Curculiox 

 I surmise there is only a short ventral cord destitute of ganglia. 



188. 



We find every variety of number between these extremes of gan- 

 glionic structure. The law which regulates the number of these ganglia 

 is still undiscovered ; for that adduced by Straus, of its being regulated 

 by the relative greater or smaller mobility of the segments, appears not 

 to suffice : he maintains, namely, in general, that the immobility of the 

 segments together causes the disappearance of all the ganglia ; and as 

 a proof he cites the families of the Dylici and Lamellicornia, whose 

 abdomen has no ganglia; but is motion less in them than in the very 

 approximate Carabodea and in the genus Lucanus ? Certainly not ! 

 This less degree of motion might be ascribed to the ventral plates, and 

 yet we find in the abdomen distinct ganglia. The number of active 

 organs found in a segment would seem rather to influence it ; at least we 

 observe the ganglia of the thorax of perfect insects always larger when 

 they are furnished with perfect organs of flight, but smaller than those 

 of the abdomen when the wings and the muscles which move them are 

 wanting, for example, Meloe *. It therefore appears preferable to 

 describe the different forms of the nervous cord of perfect insects in 

 the series of their orders and families, for within those boundaries we 

 seldom observe variations. 



The greatest number of ganglia is found in the nervous system of 

 the Orthoptera, Termites, Libellula, and many families of the Cole- 

 optera, viz. the Carabodea, Staphylini, Elaters, Buprestis, and the 

 Capricorns. In these the ventral cord exhibits immediately three 

 ganglia, which lie in the three segments of the thorax. These differ 

 in size, inter se, and indeed the smallest is found in the prothorax, the 

 largest in the metathorax, and the intermediate size in the meso- 

 thorax. The ganglion of the prothorax lies immediately in front of the 

 internal furcate branches of the sternum, at the very base of the horny 

 plate, covered by the muscles which run from here partly to the head 



* Brandt and Ratztburg, Araicitliicrc, vol. ii. part iv. PI. XVII. t'. '1. 



