$ 343. THE INSECTA. 
437 
which ramifies more or less directly; sometimes, however, several trunks 
arise from the same stigma. 
With perfect Insecta, the stigmata are nearly always situated on the 
sides of the body in the membrane connecting the two segments, being 
always wanting, however, in the membrane which unites the head and pro- 
thorax, and that between the last two abdominal segments. In many cases, 
they are covered by the borders of the segments. With the Coleoptera, the 
stigmata are often situated so high upon the back as to be concealed by the 
elytra. The number and position of the stigmata vary infinitely, and 
are not invariable in the different conditions (larva, pupa and imago) of 
even the same species. These variations are the least with the hemimeta- 
bolic Insecta. But among the Hemiptera, the Naucoridae and Nepidae 
form a remarkable exception in this respect. They have, excepting those 
of the thorax, only two stigmata at the posterior extremity of the abdomen, 
and which alone serve, probably, for respiration when these insects are in 
the water; with Nepa, and Ranatra, these anal stigmata are situated at the 
base of a long tube formed by the union of two semicanals.© The small- 
est number of stigmata, consisting of two situated adjacently at the posterior 
extremity of the abdomen, occurs with the larvae of the Dytiscidae, Stratio- 
mydae, Conopidae, and some Tipulidae and Tachinariae. Sometimes these 
two stigmata are situated at the extremity of a longer or shorter Respira- 
tory tube (Sépho), surrounded by a circle of stiff or penniform bristles. In 
some cases this siphon is very long and articulated, and can be intussus- 
cepted like the tubes of a telescope.” When these Insecta become pupae, 
these: stigmata are sometimes remarkably modified. The pupae of Culex 
lost their anal siphon, and acquire, instead, two others which are infundi- 
buliform and situated laterally between the prothorax and mesothorax.® 
The pupae of Ptychoptera respire by means of a flexible siphon situated in 
the neck. 
4 In the larvae of the Lamellicornes; see 
Sprengel, loc. cit. Tab. I. fig. 1 (larvae of Geotru- 
pes). Some Capricornes present, in their perfect 
state, a very singular organization in this respect. 
Their thoracic stigmata send off not only several 
Jarge trachean trunks, but also an infinite number 
of small branches ; see Pictet, Mém. d. 1. Soc. d. 
phys. &c. de Genéve, VIIL., 1836, p. 393, fig. 5, 6 
(Hammaticherus heros), or Ann, d. Sc. Nat. VIL. 
1837, p. 63. 
5 From this arrang t, the Dyti and 
Gyrinidae, which live in the water, must, in order 
to breathe, emerge the posterior part of their body 
to draw fresh air under their elytra, whence it is 
taken into the trach The N idae, Hy- 
drophilidae, Parnidae, and other aquatic Coleop- 
tera,respire under the water by means of a pro- 
vision of air which, after their immersion, adheres 
to the hairs of the legs. With Hydrophilus, the 
renewing of this air occurs in a very remarkable 
manner. They protrude only their antennae out 
of the water, and, bending them backwards, thus 
tablish a ii i b 
and that adhering to the under surface of the body; 
see Nitzsch, in Reil’s Arch. IL. p. 440, Taf. IX. 
6 See Roesed, Insectenbelust. III. Taf. XXII. 
XXIII.; and ZL. Dufour, Recherch. sur les Hé- 
mipt. p. 244, Pl. XVII. fig. 195, Pl. XVIII. With 
Nepe, it is true there are stigma-like rings on the 
other abdominal segments, but they are closed, and 
L. Dufour bas properly called them false stig- 
37* 
the external air - 
With the Strepsiptera, the male, as well as the apodal female 
mata. In the young age of these insects; these 
false stigmata are open and situated in two pilose 
grooves located under the belly at some distance 
from the lateral borders, and which are prolonged 
even to the end of the siphon, where they blend 
into one. The air is conducted by these grooves 
into the stigmata. 
7 By this disp of the , the larvae 
of the Dytiscidae, Culicidae and Stratiomydae, are 
obliged, in order to breathe, to rise to the surface 
of the water, where they emerge only the stigmatic 
orifices, and the air then adheres to the coronets of 
hairs on the stigmata. Many Tipulidae, such as 
Ptychoptera, communicate even more easily with 
the air by means of their long, articulated, siphon- 
tube ; see Swammerdamm, Bib. der Nat. Taf. 
XXXI. fig. 5, Taf. XXXIX. (Culex and Stratio- 
mys); Lyonet, Mém. du Mus. XIX. Pl. XVIII. 
(10) fig. 1-3 (Ptychoptera). The parasitic larvae 
of the Conopidae, and of Ocyptera of the Tachi- 
nariae, which live in the cavity of the body of Cas- 
sida, Pentatoma, Bombus and Andrena, obtain 
the necessary air for their respiration by placing 
the posterior extremity of their body, which has 
two stigmata, in contact with a stigma or trachean 
trunk of the insect in which they live: see L. Du- 
Jour, Ann. d. Sc. Nat. X. 1827, p. 255, VIL. 1837, 
p. 16, Pl. I. fig. 18. 
8 See Swammerdamm, loc. cit. 
9 See Lyonet, loc. cit. p. 4, 5. 
