-<^^m7/e« o/" Pteronarcys regalis. 4^11 



the changes of the insect, in a fold of tegument that includes branches 

 of tracheae, is thus in most perfect harmony with the character of the nerves 

 that regulate their mixed functions. The cord also gives off, between the 

 meso- and meta-thoracic ganglia, another compound branch, which first sup- 

 plies the second or mesothoracic spiracle and tracheae, and then unites with 

 the first nerve from the metathoracic ganglion, to form the second alar nerve 

 to the muscles of the second pair of wings. Besides the posterior, or gan- 

 glionic roots of the alar nerves, each ganglion gives off two others, one small 

 one to the muscles of the segment, and another, the largest nerve of each 

 ganglion in Pteronarcys and other Perlidoe, to the legs. In all insects of 

 powerful flight, the alar are the largest nerves of the trunk ; but in insects of 

 inferior power of wing, as in the Perlidoe, and more especially in those in 

 which the legs are strong and much employed, the pedal nerves, as in Ptero- 

 narcys, are much the largest. 



The aganglionic tract of the cord is as distinct in its transit over the ganglia 

 in the abdominal region as in the thorax. Each ganglion gives off a large 

 trunk to the muscles of the segment, and anterior to each, lying loosely upon 

 the aganglionic tract, a nerve passes off on each side to the false spiracles and 

 internal organs of respiration. These are the transverse or respiratory nerves, 

 which I formerly described * in the larva of the Sphinx, and which in perfect 

 insects usually become approximated to, and most closely connected with, the 

 trunks from the ganglia. They are the analogues of the compound anterior 

 roots of the alar nerves. Some of them have not united with the other trunks 

 in the anterior segments of Pteronarcys, but remain as in the larvae of Lepi- 

 doptera, thus further indicating the low type of development in this genus. 

 Others, although they have joined with the ganglionic trunks, present irre- 

 gularities in their position and distribution. The terminal ganglion of the 

 cord, as in other insects, supplies the organs of reproduction and the termi- 

 nations of the alimentary canal. 



Organs of Reproduction. — The organs of reproduction in Pteronarcys are 

 formed on the same inferior type as those of other parts of its system. They 

 differ less from those oiPerla than its other structures. The specimen I have 

 dissected proved on examination to be a male, and showed that a curious 



* Phil. Trans. 1832 and 1834. 

 3 M 2 



