_ INSECTS. : 263 
become afterwards the main trunks of the perfect Insect which are 
in connexion with the air-slits?. 
Observations have shewn that Respiration in Insects effects the 
same chemical changes of the air, as in higher creatures; respira- 
tion is more active, the need of air greater and the production of 
carbonic acid more abundant in the perfect Insect than in the 
larva. In the perfect Insect, moreover, respiration is performed 
principally by the air-slits of the thorax, which are larger than 
those of the abdomen, whilst in the larva that function is distri- 
buted more equally amongst all the stigmata. This fact is in 
connexion with the development of the thorax and with the 
mechanism for motion affixed there in the perfect Insect. Accurate 
investigations have shewn that Insects, at least under certain cir- 
cumstances, have a proper warmth, and that they can raise the 
temperature of their body remarkably by motion, or by voluntary 
acceleration of respiration?. 
The sexes are distinct in all Insects, and the eggs are not 
fertilized, as in fishes, after they are laid, but union of the sexes 
must precede the laying of the eggs if they are to prove fruitful. 
A remarkable peculiarity has been observed in Plant Lice (Aphides), 
1 Comp. on the respiratory organs of insects, besides MALFIGHI, SWAMMERDAM, 
Lyonet, Srravus and other writers already cited, C. SPRENGEL Commentarius de 
partibus, quibus Insecta spiritum ducunt, Lipsie, 1815, 4t0. cum tabulis; Suckow, 
Respiration der Insecten, insbesondere iiber die Darmrespiration der Aeschna grandis, 
Heusincer’s Zeitsch. f. die organ. Physik. 11. 1828, s. 24—29 ; BURMEISTER Handb. 
der Entomol. 1, s. 169—194 (a very careful revision of the observations of others and of 
his own) and Newport, Phil. Trans. 1836, Pt. 2, pp. 529—566 (or in Topp’s Cyclop. 
II. pp. 982—990). We refer also to the beautiful figures in Lyonur Traité an. de la 
Chenille, Pl. xx1., and Straus Anat. des anim. artic. Pl. 7, in order to give an idea of 
the minute division of the air-tubes. MARCEL DE SERRES has figured the trachee and 
air-sacs in some Orthoptera (Truxalis, Mantis) in Mém. du Muséum, tv. Pl. 15, 16. 
2 Already in 1792 VAUGUELIN had made experiments on the respiration of Insects 
(Locusta viridissima). Comp. also G. R. TREviranus, Versuche téiber das Athemholen 
der niedern Thiere, Zeitschr. f. Physiol. wv. 1831, s. 1—39, and Newport, Phil. Trans. 
l. 1., for the specific warmth, which was formerly denied by J. Davy, against whose 
observations NoBiLt and MeEtont had already advanced objections (Ann. de Chim. et 
de Physique, 1831, Octobre, pp. 207—210). All animals, LigBrG justly observes, are 
warm-blooded, but only in such as breathe by lungs (better, in mammals and birds), is 
the specific warmth entirely independent of the external temperature. Die organ. 
Chemie in ihrer Anwendung auf Physiol. u. Pathol. 1842, s.20. Comp. also BERTHOLD, 
Neue Versuche iib. d. Temperatur der kaltbliitige Thiere, Gottingen, 1825, s. 35, 36, 
8. 42. 
