§ 344. ■ THE IXSECTA. 439 



and the Pentatomidac, have varicose tracheae. With Cicada, there are 

 two of these vesicles situated at the base of the abdomen distinguished for 

 their very hirge size.'^' With Nepa, the primary trunks pass into the two 

 lateral trunks, and form transverse anastomoses which extend from one 

 side of the body to the other. In the thorax, the two lateral trunks form 

 several large vesicles, between which arise, upon the sides, two other trunks 

 which send an infinite number of very fine branches to the thoracic 

 muscles. '^^ 



With the Diptera, this system is of the first form. It often presents, 

 especially with those having a large andshort abdomen, vesicular dilatations 

 of which there are two, situated at the base of the abdomen, very large 

 and distinct, sometimes filling nearly the whole abdominal cavity.''^' It is, 

 moreover, with the larvae of this order, that this form of tracheae is most 

 completely represented. The two lateral trunks are connected by the same 

 number of transverse anastomoses as there are segments of the body.**^' 



With the Lepidoptera in all their states, this system is also of the first 

 form.^*' With the imagines of some Sphingidae, Bombycidae and Noctui- 

 dae, whose flight is continual, there are numerous vesicular dilatations and 

 appendages of the tracheae.''*' 



The tracheae of the Hymenoptera, which, throughout, are of the first 

 form, send off from their two principal trunks numerous transverse anas- 

 tomoses, and usually present vesicular dilatations at many points.'^"' Of 

 these last, those situated on the abdominal portion of the two trunks are 

 very large, and often contiguous, so that the trunk to which they belong 

 appears like a large sac constricted from point to point.'"* Sometimes 

 there are only two of these vesicles, which are distinguished from the rest 

 by their enoi-raous volume, situated at the base of the abdomen.*^-' With 

 the larvae, there are found, pretty commonly, two main trunks connected 

 by transverse communicating tubes. '^^* 



4 See Burmeister, Handb. &c. II. Taf. I. fig. ages is reduced to two large aeriferous reservoirs 

 10-12 (Coccidae) ; L. Dufour, Recherch. loc. cit. situated in tlie thorax ; see Suckow, Anat. physiol. 

 PI. XVII. fig. 194 {Tetyra), and Cams, Analelit. Untersuch, p. 36, Taf. VII. fig. 30 (jOastropacha 

 &c. p. 156 (Cicada). pini). 



5 See L. Dufour, Recherch. &c. p. 244, PI. lU These dilatations are wanting with the Cynipi- 

 XVIII. dae, Chalcididae, and some Iclineivmonidae. For 



6 With the Muscidae, Syrphidae, Tabanidae, the trachean system of the Hymenoptera in general, 

 Asilidae, Leptidae, &c. For the trachean system see L. Dufour, Recherch. sur les Orthopt. i5. 

 of the larva and pupa of Sarcophaga haemnr- 374.* 



rhoidalis, see L. Dufour, M6m. presentes, &c., 11 With the Apidae, Andrenidae, Vespidae and 



IX. p. 572, PI. II. Bembecldae ; see Brandt and Ratzeburg, Mediz. 



7 Swammerdamm, Bib. der Nat. Taf. XL. fig. Zool. II. Taf. XXV. fig. 30 {Apis meUifica), and 

 1 {\a,rva. of a. Stratiomys); Bouchi, Naturgeseh. Newport, PhUos. Trans. 1836, PI. XXXVI. or 

 d. Insekt. Taf. VI. fig. 1 (larva of an Anthomyia), Cyclop. &c. II. fig. 436 (Bombus terrestris). 



and L. Dufour, Ann. d. Sc. Nat. XII. 1839, PI. VI With many of the Tenthredinidae, with Myr- 



I.-III. mosa, Scolia, Crabro, Pompilus, Sphex, &c. 



8 Lyonet, Traits, Pi. X. XI. (larva of Cossus IS See Stvammerdmrnm , Bib. der Nat. Taf. 

 ligniperda). While the Syrphidae and Muscidae XXIV. fig. 1 (larva of a bee). According to the 

 are passing into their pupa-state, the posterior observations of Ratzeburg (Die Ichneumon, d. 

 stigmata disappear, the two anterior ones alone Forstinsekt, p. 63, 81, Taf. IX.), the parasitic 

 remaining active. With the Syrphidae these last larvae of Microgaster and Anomalon are very 

 often appear as two short tubes inserted on the cer- singular. When young, they have no traces of 

 vical region. tracheae, and respire, perhaps, by means of a cau- 



y See Sprengel, loc. cit. Tab. III. fig. 24 (Sphinx dal appendage enveloped by a thin membrane. 

 ligustri). Sometimes the number of these append- 



* [ § 344, note 10. J See Newport (On the form- vesicles serve chiefly to enable the Insect to alter 



ation and use of the air-sacs and dilated tr-acheae its specific gravity at pleasure during flight, and 



in Insects, Trans. Linn. Soc. June, 1847) ; these thus diminish the muscular e.xertion required dur- 



sacs are fonred during the metamorphoses of the ing these movements. — Ed. 

 insect, and I- wlopts the view of Hunter, that the 



