§ 344. THE INSECTA. 439 
and the Pentatomidae, 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 trumks 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.“ , 
4See Burmeister, Handb. &c. IT. Taf. I. fig. 
10-12 (Coccidae) ; L. Dufour, Recherch. loc. cit. 
Pl. XVII. fig. 194 (T'etyra),, and Carus, Analekt. 
&c. p. 156 (Cicada). 
5 See L. Dufour, Recherch. &c. p. 244, Pl. 
XVIII. 
6 With the Muscidae, Byrphidhe, Tabanidae, 
Asilidae, Leptidae, &c. For the trachean system 
of the larva and pupa of Sarcophaga haemor- 
rhoidalis, see L. Dufour, Mém. présentés, &c., 
IX. p. 572, Pl. If. 
7 Swammerdamm, Bib. der Nat. Taf. XL. fig. 
1 (larva of a Stratiomys) ; Bouché, Naturgesch. 
d. Insekt. Taf. VI. fig. 1 (larva of an Anthomyia), 
and L. Dufour, Ann. d. Sc. Nat. XII. 1839, Pl. 
L 
8 Lyonet, Traité, Pl. X. XI. (larva of Cossus 
ligniperda). 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. ITI. fig. 24 (Sphinz 
ligustri). Sometimes the number of these append- 
* [ § 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 forned during the metamorphoses of the 
insect, and ¥« adopts the view of Hunter, that the 
ages is reduced to two large aériferous reservoirs 
situated in the thorax ; see Sucicow, Anat. physiol. 
Untersuch. p. 36, Taf. VII. fig. 30 (Gastropacha 
pini). 
10 These dilatations are wanting with the Cynipi- 
dae, Chalcididae, and some Ichneumonidae. For 
the trachean system of the Hymenoptera in general, 
see L. Dufour, Recherch. sur les Orthopt. p. 
374* 
11 With the Apidae, Andrenidae, Vespidae and 
Bembecidae ; see Brandt and Ratzeburg, Mediz. 
Zool. Il. Taf. XXV. fig. 30 (Apis mellifica), and 
Newport, Philos. Trans. 1836, Pl. XXXVI. or 
Cyclop. &c. IL. fig. 436 (Bombus terrestris). 
12 With many of the Tenthredinidae, with Myr- 
mosa, Scolia, Crabro, Pompilus, Sphea, &c. 
18 See Swammerdamm, Bib. der Nat. Taf. 
XXIV. fig. 1 (larva of a bee). According to the 
observations of Ratzeburg (Die Ich 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. 
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. — Ep. 
