‘ 
438 THE INSECTA. § 344, 
pupae, respire by two stigmata situated on the sides of the cephalo- 
thorax. 
Most of the acephalous larvae 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, the two posterior stigmata consist of two siphons, 
which are often fused into one.0? The larvae of the Coccidae have only 
four stigmata 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. 
§ 844. 
_ 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 two 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- 
-anastomose by transverse trunks. 
Often these two forms of tracheae coéxist 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 
Pediculidae, 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 Wiegmann’s Arch. 1843, 
I. Taf. VII. 
11 See Bouché, Naturgesch. d. Insekt. Taf. V. 
VI.; Z. Dufour, Ann. d. Sc. Nat. XII. 1839, 
Pl. II. TIL., and XIII. 1840, Pl. IIL. and I. 1844, 
PIXVI.(Tachina, Anth i , Sapro~ 
myza, Piophila, &e.). 
12 The siphon is very long, articulated, and situ. 
ated at the extremity of the body with the larvae of 
Eristalis ; see Réaumur, Mém. loc. cit. IV. Pl. 
XXX. XXXII. 
wea See Burmeister, Handb. &c. II. Taf. I. fig. 
-12. 
1 See, beside the works of Burmeister and La- 
cordaire, the work of Marcel de Serres, in the 
Mém. du Mus. IY. p. 313. 
Yray, 
2 With the Poduridae, the six trachean branches 
given off from the two main trunks, have each an 
oval dilatation ; see Nicolet, loc. cit. p. 47, Pl. IV. 
3 Guerin (Ann. d. Sc. Nat. V. 1836, p. 374) 
thinks that the trachean system is wanting with 
Machilis ; but this must be incorrect, for Bur- 
meister (Isis, 1834, p. 137) has observed this sys- 
tem with Lepisma, with which it had for a long 
time before been sought in vain. I have very dis- 
tinctly observed it in Machilis, as well as in Le- 
pisma, and its organization is the same in both. 
The vesicles which, with Machilis, are situated on 
the sides of the abdominal appendages, and which 
Guérin thinks are respiratory organs, must -have 
another function. : 
