436 THE INSECTA. $ 343, 
pteryz are distinguished for having three long, lamelliform branchiae, with 
a rounded extremity, and situated vertically upon the posterior part of the 
abdomen. 
The trachean branchiae of Aeschna, Libellula, and the other Libellu- 
lidae, are formed upon a wholly different plan. They are situated in the 
very large rectum, and’ consist of numerous epithelial folds which are 
traversed by a great number of very fine branches of many large trachean 
trunks. The rectum is, moreover,, invested by a very highly-developed 
muscular tunic, and its orifice has three pyramidal valves which regulate 
the entrance and the escape of the water required for respiration. 
Finally, the larvae of Gyrinus have a pair of long branchiae upon the 
sides of each of the first seven abdominal segments, and two pairs on those 
of the eight.“ 
§ 343. 
The tracheae most universal with Insecta are those termed Pulmonary, 
which are characterized by the presence of stigmata (Spiracula). These 
last are round orifices or narrow two-lipped openings, situated at various 
points on the external surface of the body, and which, with many soft-skinned 
Insecta, are surrounded by a horny ring. Usually, their borders are fringed 
with small, short, simple or pinnate hairs,” and can be opened and shut by 
means of an internal muscular apparatus; this last is sometimes attached 
to two inwardly-projecting horny plates. By these means, many Insecta 
have well-marked respiratory motions, especially of the abdomen. 
With the larvae of the Lamellicornes, the stigmata have a peculiar 
organization. They are closed by a horny membrane whose semilunar 
borders are cribriform for the free passage of air.© 
The larvae of the Oestridae have two large stigmata, covered each by a 
similar plate or membrane, at the extremity of the abdomen; and with 
some larvae of the Muscidae, the posterior stigmata are closed in the same 
manner, excepting that the membrane is perforated by three very distinct 
openings. 
Each stigma is usually the entrance of only a single trachean trunk 
, 
8 Roesel, Insectenhelust. II. Insecta aquatica, 
Cines, IL. Taf. IX. XI.; and Carus, Entdeck. &c. 
Taf. I. 
9 Roesel, loc. cit. Taf. ITI—VIII. and Suckow, 
in Heusinger’s Zeitsch. II. p. 35, Taf. I. If. 
10 Roesel, loc. cit. IIL. Taf. XXXI. and De- 
geer, Abhandl. IV. Taf. XIII. Further researches 
are required to decide if the penniform appendages, 
situated on the sides of the abdominal segments of 
certain larvae of the Hydrophilidae, are really 
trachean branchiae. But it appears to me that, 
with these larvae, the pulmonary and trachean 
branchiae are confounded ; see Roesel, Insecten- 
belust. II. Insect. aquat. Class. I. Taf. LV. and 
Lyonet, Mém. du Mus. XVIII. Pl. XXIII. (12), 
tig. 47 (Hydrophilus caraboides. 
1L. Dufour, Ann. d. Sc. Nat. VIII. 1826, p 20, 
Pl. XXI. ' 
2 The Locustidae, Libellulidae, avd other Ortho- 
ptera, make true movements of inspiration and ex- 
piration, by alternately dilating and contracting 
the abdominal segments. With the Apidac, Ves- 
pidae, and other Hymenoptera, the alternate con- 
tractions and dilatations of the #1¢ ominal cavity are 
due to the protractile and retractile movements of 
the abdominal segments. Many Lamellicornes 
make these respiratory movements before flying, 
probably that they may fill their trachean system 
with air, 
3 Sprengel (loc. cit. p. 9, Tab. I.) has described. 
very correctly the stigmata of the Lamellicornes. 
Treviranus (Die Erschein. und Gesetze d. Organ. 
Lebens, I. p. 258) thinks that these lamellae are not. 
perforated and that the air enters these tracheae by 
endosmose, although Burmeister (Iandb. &c. I. 
p. 172) says he has observed a single central open- 
ing. I have been unable to confirm the statement 
of Sprengel, and think that these perforations 
might easily elude the observation, from their being 
concealed beneath a kind of net-work on the exter= 
nal surface of these lamellae. L. Dufour (Ann. 
d. Sc. Nat. XVIII. 1842, p. 172, Pl. IV. fig. 7) has 
also misapprehended the stigmata of the larvae of 
Cetonia; for that which he has described as a 
transverse fissure is only a fold, due to a pressure 
exercised during the manipulation, on the horny 
Jamella which norr’- lly is convex and imperforate 
in its centre. 
