Affinities of Pteronarcys regalis. 427 



first mention that, like a very large proportion of the Neuroptera, it is en- 

 tirely aquatic in its larva and pupa (fig. 2) states, and, consequently, that its 

 respiration is then wholly branchial ; but that in its imago or perfect state 

 (fig. 1) it not only possesses true spiracles and tracheae for atmospheric respi- 

 ration, like other winged insects, but also retains the branchiae of its earlier 

 conditions, both on its thoracic and its abdominal segments, fitted for aquatic 

 respiration. Now, although branchiae invariably perform similar functions in 

 all insects which possess them, they have hitherto been found only in the. larva 

 and pupa states. They are situated on different parts of the body in different 

 genera, and, as naturalists are aware, exist, sometimes even in different species 

 of the same genus, under different forms. In the true Libellulce they are anal, 

 and are contained within a cloaca or cavity posterior to the termination of 

 the alimentary canal, into which the respired water is drawn by the insect at 

 eacli inspiration, and is expelled from it in expiration. When this act takes 

 place by a forcible effort on the part of the insect, it urges the body forwards, 

 and thus becomes an act of progression. In the Jgrionidce the branchiae con- 

 sist of long caudal plates, through which the blood circulates to be submitted 

 to aeration. In the Ephemeridce, as in Ephemera vulgata, the branchiae are 

 both caudal and abdominal, each ring of the abdomen being furnished with 

 bipectinated, projecting cilia, folded over the upper surface of the body. In 

 the genera Palingenia and Baetis of M. Pictet and Dr. Leach the abdominal 

 branchiae are both pectinated and lamellate, the lamellae being folded upwards 

 on the dorsal surface of the body. In Potamanthus cinctus, according to Pictet *, 

 they are simply dendrical and setaceous, the setaceous terminations of the in- 

 cluded tracheae being the apices of the branchiae ; while in some few spe- 

 cies of the same genus, as in Potamanthus erythrocephaliis, they are lamellate, 

 as they are also in Che. In the whole of the true Phryganidce, Mystacidce, 

 Trichostomes and Sericostomes, the branchiae are simple, hair-like structures, 

 which cover the sides and dorsal surface of the abdomen, and these are re- 

 tained in the pupa state as the respiratory organs. In Rhyacophilus vulgaris f 



* Hist. nat. des Ins. Neuropt. Seconde Monogr., Fam. des Eph^mdrines. Geneve, 1843, pi. 28. 

 figs. 1 & 2. p. 198. 



t Recherches pour servir h. I'Histoire et TAnatomie des Phryganides. Par J. F. Pictet. Genfeve, 

 4to, 1834. pi. 15. fig. 1. 



