Affinities of Pteronarcys regalis. . 497 
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 tracheze for atmospheric respi- 
ration, like other winged insects, but also retains the branchia: of its earlier 
conditions, both on its thoracic and its abdominal segments, fitted for aquatic 
respiration. Now, although branchize 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 Libellule 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 
each 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 Agrionide the branchie con- 
sist of long caudal plates, through which the blood circulates to be submitted 
to aération. In the Ephemeride, as in Ephemera vulgata, the branchie 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 Baétis of M. Pictet and Dr. Leach the abdominal 
branchize are both pectinated and lamellate, the lamellz 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 trachez being the apices of the branchiz; while in some few spe- 
cies of the same genus, as in Potamanthus erythrocephalus, they are lamellate, 
as they are also in Cloé. In the whole of the true Phryganide, Mystacide, 
Trichostomes and Sericostomes, the branchiz 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 t 
* Hist. nat. des Ins. Neuropt. Seconde Monogr., Fam. des Ephémérines. Genève, 1843, pl. 28. 
figs. 1 & 2. p. 198. 
T Recherches pour servir à l'Histoire et l'Anatomie des Phryganides. Par J. F. Pictet. Genève, 
‘to, 1834, pl. 15, fig. 1. ; 
