§344. 



THE INSECTA. 



439 



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

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

 their very large 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 and short 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 enormous 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. 

 10-12 (Coccidae) ; L. D;tfour, Recherch. loc. cit. 

 PI. XVII. fig. 194 {Tetyra), and Cams, Analekt. 

 &c. p. 156 (Cicada). 



5 See L. Dufour, Kecherch. &c. p. 244, PI. 

 XVIII. 



6 W^ith the Muscidae, Syrpliidae, Tabanidae, 

 Asilidae, Leptidae, &c. For tlie tracheal! system 

 of the larva and pupa of Sarcophaga haemnr- 

 rhoida/is, see L. Dufour, Mem. presenles, &c., 

 IX. p. 572, PI. II. 



7 SwammeTdamm, Bib. der Nat. Taf. XL. fig. 

 1 (larva of a Stratiomys) ; Bouclte, Naturgesch. 

 d. Insekt. Taf. VI. fig. 1 (larva of an Anthomyia), 

 and L. Dufour, Ann. d. Sc. Nat. XU. 1839, PI. 



i.-ni. 



8 Lyonet, Traits, PI. X. XI. (larva of Cossus 

 Hgniperda). While the Syrphidae and Muscidae 

 are passing into their pupa-state, the posterior 

 stigmata disappear, the two anterior ones alone 

 remaining active. With the Syrphidae these last 

 often appear as two short tubes inserted on the cer- 

 vical region. 



9 See Sprengel, loc. cit. Tab. III. fig. 24 {Sphinx 

 ligustri). Sometimes the number of these append- 



ages Is reduced to two large aeriferous reservoirs 

 situated in the thorax ; see Suckow, Anat. physiol. 

 tJntersuch. p. 36, Taf. VII. fig. 30 (Gastropacha 

 pini). 



10 These dilatations are wanting with the Cynipi- 

 dae, Chaleididae, and some Ichneumonidae. For 

 the trachean system of the Hymenoptera in general, 

 see L. Dufour, -Recherch. sur lea Orthopt. p. 

 374.* 



11 With the Apidae, Andrenidae, Vespidae and 

 Bembecldae ; see Brandt and Ratzeburg, Mediz. 

 Zool. II. Taf. XXV. fig. 30 (Apis meUiJica), and 

 Newport, Pliilos. Trans. 1836, PI. XXXVI. or 

 Cyclop. &c. II. fig. 436 (Bombus terrestris). 



12 With many of the Tenthredinidae, with Myr- 

 mosa, Sco/ia, Crabro, Pompilus, Sphex, &c. 



W See Swammerdamm, Bib. der Nat. Taf. 

 XXIV. fig. 1 (larva of a bee). According to the 

 observations of Ratzeburg (Die Ichneumon, d. 

 Forstinsekt. p. 63, 81, Taf. IX.), the parasitic 

 larvae of Microgaster and Anomalon are very 

 singular. When young, they have no traces of 

 tracheae, and respire, perhaps, by means of a cau- 

 dal appendage enveloped by a thin membrane. 



* [ § 344, note 10.] See Newport (On the form- 

 ation and use of the air-sacs and dilated tracheae 

 in Insects, Trans. Linn. Soc. June, 1847) ; these 

 sacs are formed during the metamorphoses of the 

 insect, and he adopts the view of Hunter, that the 



vesicles serve chiefly to enable the insect to alter 

 its specific gravity at pleasure during flight, and 

 thus diminish the muscular exertion required dur- 

 ing these movements. — Ed. 



