^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 diiferent 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, Gonopidae, and some Tipulidae and Tachinariae. Sometimes these 

 two stigmata are situated at the extremity of a longer or shorter Respira- 

 tory tube (Sipho), surrounded by a circle of stiff or penniform bristles. In 

 some cases this siphon is very long and articulated, and can be intussu.s- 

 cepted like the tubes of a telescope.*'"' When these Insecta become pupae, 

 these stigmata are sometimes remarkably modified. The pupae of Culex 

 lose their anal siphon, and acquire, instead, two others which are infundi- 

 buliform and situated laterally between the prothorax and niesothorax.'**' 

 The pupae of Ptyckoptera respire by means of a flexible siphon situated in 

 the neck.*-'' With the Strepsiptera, the male, as well as the apodal female 



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 

 Btate, a very singular organization in this respect. 

 Their thoracic stigmata send off not only several 

 large trachean trunks, but also an inlinite number 

 of small branches; see Pictet, Mem. d. 1. Soc. d. 

 phya. &c. de Geneve, VII., ISIiti, p. 393, fig. 5, 6 

 (Hammatic/ierus heros), or Ami. d. Sc. Nat. Vil. 

 1837, p. 63. 



s From this arrangement, the Dytiscidae 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 tracheae. The Notonectidae, 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 Hydrophilas, tlie 

 renewing of this air occurs in a very remarkable 

 manner. They protrude only their antennae out 

 of the water, and, bending them b.-vckwards, thus 

 establish a communication between the e.\ternal air 

 and that adhering to the under surface of the body; 

 see Nitzsch, in ReWs Arch. II. p. 440, Taf. IX. 



G See Roesel, Insectenbelust. III. Taf. XXII. 

 X.XIII.; and L. Dufour, Recherch. sur les Ile- 

 mipt. p. 244, PI. XVII. fig. 195, PI. XVIII. With 

 Nepa, it is true there are stigma-like rings on the 

 other abdominal segments, but they are closed, and 

 L. Dufour has proi)erly called them false stig- 



37=* 



mata. In the young age of these insects; these 

 false stigmata are open and situated in two pilojie 

 grooves located under the belly at some distiince 

 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. 



't By this disposition of the stigmata, 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 

 Ptyckoptera, communicate even more easily with 

 th--' 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, Mem. du Mus. XIX. PI. XVIIl. 

 (10) fig. 1-3 (Ptyckoptera). 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- 

 four, Ann. d. Sc. Nat. X. 1827, p. 255, VU. 1837, 

 p. 16, PI. I. fig. 13. 



S See Swammerdamm, loc. cit. 



9 See Lyonet, loc. ciU p. 4, 5. 



