OF INSECTS. 177 



in the abdomen,, the nerves descend in long threads 

 from the thoracic knots. 



Mr. Newport, following up a discovery of Lyonnet's, 

 has lately made us acquainted with a delicate system 

 of nervous branches appropriated to the respiratory 

 organs, which lies above the ventral chain, following 

 it without interruption through its whole extent. It 

 consists of a very slender thread placed on the median 

 line of the longitudinal cords, but not easily distin- 

 guishable except where these are separated ; it then 

 seems to spring from the inferior angle of each gan- 

 glion, although, in reality, it passes above it. At 

 a little distance from that point it divides into two 

 branches, which extend laterally in opposite directions. 

 No knotty expansion is visible in caterpillars, but in 

 Carabus and Gryllus there is a distinct one at each 

 dichotomous division of the filet, especially in the 

 thorax, where these nerves are most highly developed. 

 As the changes which they undergo in the course of 

 metamorphoses do not correspond to those that take 

 place in the ventral chain, which always tends, with 

 every successive development, to a higher state of 

 concentration, Mr. Newport regards these nerves as 

 forming a separate system, and he has named them 

 the auxiliary, transverse, or respiratory nerves.* 



The preceding descriptions will be better under- 

 stood by the illustrative figures on Plate IV. Fig. 1 

 represents the nervous tree of the common cockchafer, 

 which may be regarded as the type of that division 



* Philosophical Transactions for 1832-4. 

 M 



