^M'i 



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 m the membrane connecting the two segments, being 

 always wanting, however, in the membrane which unites the head and pro- 

 Ihorax, and that between the last two abdominal segments. In many cases, 

 they are covered by the borders of the segments. ^V'ith 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 Naueoridae 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 [Sipho), surrounded by a circle of stiff or pennifonn 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 

 lose 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.*"' With the Strepsiptera, the male, as well as the apodal female 



4 In the larvae of the Lamellicornes ; see mata. In the young age of these insects; these 

 Sprengel, loc. cit. Tab. I. fig. 1 (larvae of Geotru- false stigmata are open and situated in two pilose 

 pes). Some Capricornes present, in their perfect grooves located under the belly at some distance 

 state, a very singular organization in this respect, from the lateral borders, and which are prolonged 

 Their thoracic stigmata send off not only several even to the end of the siphon, where they blend 

 large trachean trunks, but also an infinite number intfi one. The air is conducted by these grooves 

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



phys. &c. de Gendve, VII., 1836, p. 393, fig. 5, 6 ''By this disposition of the stigmata, the larvae 



{Hammaticherus heros), or Ann. d. Sc. Nat. Vll. of the Dytiscidae, Culicidae and Stratiomydae, are 



1837, p. 63. obliged, in order to breathe, to rise to the surface 



5 From this arrangement, the Dytiscidae and of the water, where they emerge only the stigmatic 

 Gyrinidae, which live in the water, must, in order orifices, and the air then adheres to the coronets of 

 to breathe, emerge the posterior part of their body hairs on the stigmata. Many Tipulidae, such as 

 to draw fresh air under their elytra, whence it is Ptychoptera, communicate even more easily with 

 taken into the tracheae. The Notonectidae, Hy- the air by means of their long, articulated, siphon- 

 drophilidae, Parnidae, and other aquatic Coleop- tube ; see Swammerdainm, Bib. der Nat. Taf. 

 tera, respire under the water by means of a pro- XXXI. fig. 5, Taf. XXXI.X. {Culex and Stratio- 

 vision of a.\v which, after their immersion, adheres mys) ; Lyonet, Mem. du Mus. XIX. PI. XVIII. 

 to the hairs of the legs. With Hydrop/iihis, the (10) fig. 1-3 {Ptychoptera). The parasitic larvae 

 renewing of this air occurs in a very remarkable of the Conopidae, and of Ocyptera of the Tachi- 

 manner. They protrude only their antennae out nariae, which live in the cavity of the body of Gas- 

 öl the water, and. bending them backwards, thus sida, Pentatoma, Bombus and Andrena, obtain 

 establish a communication between the external air the necessary air for their respiration by placing 

 and that adhering to the under surface of the body; the posterior extremity of their body, which ha» 

 see Nitzsch, in Reil's Arch. II. p. 440, Taf. IX.. two stigmata, in contact with a stigma or trachean 



fj See Roesel, Insectenbelust. III. Taf. X.XII. trunk of the insect in which they live : see L. Du- 



XXIII.; and L. Du four, Recherch. sur les He- four, Ann. d. Sc. Nat. X. 1827, p. 2Ö5, VII. 1837, 



mipt. p. 244, PI. XVII. fig. 19.5, PI. XVIII. With p. 16, PI. I. fig. 13. 



Nepa, it is true there are stigma-like rings on the s See Swammerdamm, loc. cit. 



other abdominal segments, but they are closed, and 9 See Lyonet, loc. cit. p. 4, 5. 

 L. Dufour has properly called them false stig- 



37# 



