438 THE INSECTA. ^ <§> 344. 



pupae, respire by two stigmata situated on the sides of the cephalo- 

 thorax/"' 



Most of the acephalous hirvae of Diptera have only four stigmata, of 

 which two are situated on the truncated extremity of the abdomen, and the 

 two others, smaller, upon the sides of the second segment of the body. 

 These last have sometimes a tubular form, and with some species, are even 

 divided digitiformly at their extremity.^"' With the larvae of many Syr- 

 phidae and Tachinariae, t^e two posterior stigmata consist of two siphons, 

 which are often fused into one/'-^ The larvae of the Coccidae have only 

 four ftigmata situated on the under side of the middle portion of their 

 body.'^'^' Most of the larvae of the Coleoptera, Hymenoptera, Lepidoptera, 

 as well as the cephalous ones of the Diptera, have numerous stigmata situ- 

 ated on each side in the middle of the segments of the body, and which 

 are never wanting, constantly, except with the second and third thoracic, 

 and the last abdominal segments. 



§ 344. 



The numerous differences of the trachean system ^' in the various 

 families of the Insecta may be classed under two principal forms. 



1. With the first and most common, there are tAvo large lateral trunks 

 upon the sides of which open trunks which arise from the stigmata. From 

 these lateral trunks branch off" tracheae to the various parts of the body. 



2. With the second form, the trunks which arise from the stigmata or 

 trachean branchiae, directly ramify over the organs, but give off, both 

 forwards and backwards, branches of communication to the neighboring 

 trunks. The branches of one and the same segment frequently inter- 

 anastoraose by transverse trunks. 



Often these two forms of tracheae coexist in the same individual. In 

 many cases, the secondary tracheae, in opening into the main trunks, are 

 dilated into a large vesicle, or have upon their course numerous similar 

 vesicles which give the whole system a varicose aspect. 



Among the Aptera, the trachean system is of the first form with the 

 Pedieulidae, Nirmidae, and Poduridae.*-^ But the Lepismidae form an 

 exception in this respect, each of their stigmata opening into a trunk, 

 which, without anastomosing with the neighboring trunks, is isolatedly 

 ramified.'^' 



With the Hemiptera, the trachean system presents many modifications. 

 The trunks arising from the stigmata, sometimes ramify without anastomos- 

 ing, and sometimes open into two lateral trunks. The musical Cicadidae 



10 See my Memoir in Wie^mann's Arch. 1843, 2 With the Poduridae, the six trachean branches 



I. Taf. VII. given off from the two main trunlis, have each an 



U See Bouche, Naturgesch. d. Insekt. Taf. V. oval dilatation ; see Nicolet, loc. cit. p. 47, PI. IV. 



VI. ; L. Dufour, Ann. d. Sc. Nat. XII. 1839, fig. 3. 



PI. II. III., and XIII. 1840, PI. III. and I. 1844, 3 Gu-irin (Ann. d. Sc. Nat. V. 1836, p. 374) 



'P\.Xyi.{Tac.hina,Anthomyia,Helomyza,Sapro- thinks that the trachean system is wanting with 



myza, Piopliila, &c.). Machilis ; but this must be incorrect, for Bur- 



y.i The siphon is very long, articulated, and situ- meister (Isis, 1834, p. 137) has observed this sys- 



ated at the extremity of the body with the larvae of tern with Lepisina, with which it had for a long 



Eris talis ; see Reaumur, Mem. loc. cit. IV. PI. time before been sought in vain. I have very dis- 



XXX. XXXII. tinctly observed it in Machilis, as well as in Le- 



13 See Burmeister, Handb. &c. 11. Taf. I. fig. pisma, and its organization is the same in both. 



10-12. The vesicles which, with Machilis, are situated on 



1 See, beside the works of Burmeister and La- the sides of the abdominal appendages, and which 



cordaire, the work of Marcel de Serres, in the Guerin thinks are respiratory organs, must have 



M6m. du Mus. IV. p. 313. another function. 



