436 



THE INSECTA, 



§ 34S. 



pteryx 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 diiferent plan. They are situated in the 

 very large rectum, and consist of numei'ous 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.*'"' 



§ S43. 



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 Rnesel, Insectenbelust. II. Insecta aquatica, 

 Class. II. Taf. IX. XI.; and Cams, Eutdeck. &c. 

 Taf. I. 



9 Roesel, loc. cit. Taf. III.-VIII. and Suckow, 

 in Heusinser''s Zeitsch. II. )>. 35, Taf. I. II. 



10 Roesel, loc. cit. III. Taf. XXXI. and De- 

 geer, Abhandl. IV. Taf. XIII. Further researches 

 are required to decide if the peniiirörm appendages, 

 situated on the sides of the abdominal segments of 

 certain larvae of the IIydroi)hilidae, are really 

 trachean branchiae. But it appears to me that, 

 with these larvae, the pulmonary and trachean 

 branchiae are confovmded ; see Roesel, Insecten- 

 belust. II. Insect. a(iuat. Class. I. Taf. IV. and 

 Li/onet, Mem. du Mus. XVIII. PI. XXIII. (12), 

 tig. 47 {Hydrophilus carahoides.) 



1 /.. J)ufour, Ann. d. Sc. Nat. VIII. 1826, p 20, 

 PI. XXI. 



'■i The Locustidae, Libellulidae, a'"l other Ortho- 

 ptera, make true movements of ins,..iration and ex- 

 piration, by alternately dilating and contracting 

 the abdominal segments. With the Apidac, Ves- 

 pidae, and other Jlymenoptera, the alternate con- 

 tractions and dilatations of I'je 'S>K ominal cavity are 



due to the protractile and retractile movements of 

 the abdominal segments. Many Lamellicornea 

 make these respiratory movements before flying^ 

 probably that they may fill their trachean system 

 with air. 



ä Sprengel (loc. cit. p. 9, Talj. 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 liy 

 endosmose, although Hiinneister (Ilanill). &c. I. 

 p. 172) says he has ohscrvcil a single central open- 

 ing. I have been unable to confirm the statement 

 of Sprengel, and think that these pcrtnratii>na 

 might easily elude the observation, from their being 

 concealed beneath a kind of net-work on the exter- 

 nal surface of these lamellae. L. Diifour (Aim. 

 d. Sc. Nat. XVIII. 1842, p. 173, PI. IV'. fig. 7) has 

 also misapprehended the stigmata of the larvae of 

 Cetotiia ; for that which he has described as a 

 transverse fissure is only a fold, due to a pressure 

 exercised during the manipulaticm, on the horny 

 lamella which norr- ,lly is convex and imperforate 

 iu its centre. 



