Page:Jardine Naturalist's library Entomology.djvu/183

Rh 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 distinguishable except where these are separated; it then seems to spring from the inferior angle of each ganglion, 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 understood 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