132 
NEUROPTERA. 
dee, Helodes (Dascillidce), Culex, Dixa and Anopheles (Culicidce), Tipu- 
lidee, Stratiomys, Tabanidce, Syrphidce, and Sciomyzidee ; in these it 
obtains in the larva, and not always in the pupa, though in Stratiomys 
and Hcemonia, for instance, the pupa also exhibits it. In a few, we get 
the complementary state, in which the anterior spiracle alone is func¬ 
tional, as in the pupae only of Culicidce, Chironomidce and Dixidce. 
In the above there have been in all cases at least one spiracle func¬ 
tional and the normal tracheal system. In those that follow, there are 
no functional spiracles, unless one of the above systems is combined with 
it; most larvae exhibit one of the above modifications, with one or sev¬ 
eral of the following, though the latter may occur alone or in combination 
with each other. Tracheal gills alone, with no other definite system, 
occur in a number of larvae ; in these the skin is produced into thin- 
walled tubular structures in which the body-fluid circulates, in which 
there are tracheae, and which function as gills since they absorb 
(or are supposed to absorb) oxygen but are tracheal and not true 
gills since the air is passed into the trachea and not, apparently, 
into the “blood” system. Such gills take many forms but are common¬ 
ly tubular or paddle-like, in tufts, in spongy masses ; they occur in 
larvae which do not come to the surface but live wholly in the water at 
some depth usually, as in the Perlidce, Ephemeridce, Sialidce, Sisyra 
( Hemerohiidce ), Haliplidce , and Calopterygides (Odonata), and in the sub¬ 
families Phryganeides, Sericostomatides and Leptocerides of the Phryga- 
neidee. These gills may be on the eight basal abdominal segments 
(Haliplidce ), on the seven basal abdominal segments (Sialidce), on the 
apex of the abdomen (Chironomidce), Corethra (Culicidce), Simulium, 
and the Calopterygine division of Odonata, on the base of the 
abdomen (Perlidce, some Ephemeridce) or on the whole abdomen 
( Gyrinidce, Phryganeidce). 
Accessory tracheal gills also occur, in combination with a spiracular 
or other combination, as in Dixa, Culex, Mochlonyx and Helodes. Such 
accessory gills are extremely common and cannot always be easily dis¬ 
tinguished. Rectal respiration is another modification of tracheal res¬ 
piration, in which water is taken into and discharged from the rectum, 
which is set extremely densely with trachese and functions as a “water- 
lung ” or gill. Odonata (exc. Calopterygidce) are the best examples, the 
very young Chloeon ( Ephemeridce) is another and both Culex and Cera - 
topogon also exhibit it. 
There are finally some modifications in which tracheae play no direct 
part; the skin possibly functions as a “gill ’’ in many of the young larval 
forms, in which there is no other system developed ; this is a matter of 
conjecture largely, but there is no other available explanation of the res¬ 
piration of many young aquatic forms. Some Phryganeidce and Perlidce 
never exhibit any other respiration throughout larval life, and it is pre¬ 
sumed the air is obtained through the skin. 
