Affinities of Pteronarcys regalis. 441 
the changes of the insect, in a fold of tegument that includes branches 
of tracheze, 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 tracheæ, 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 Perlide, to the legs. In all insects of 
powerful flight, the a/ar are the largest nerves of the trunk ; but in insects of 
inferior power of wing, as in the Perlide, 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 a/ar 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 Pferonarcys are 
formed on the same inferior type as those of other parts of its system. They 
differ less from those of Perla than its other structures. The specimen I u- 
dissected proved on examination to be a male, and showed that a curious 
* Phil. Trans. 1832 and 1834. 
3M2 
