INSECTS. 263 



become afterwards the main trunks of the perfect Insect which are 

 in connexion with the air-slits 1 . 



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 ivarmth, and that they can raise the 

 temperature of their body remarkably by motion, or by voluntary 

 acceleration of respiration 2 . 



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 MALPIGHI, SWAMMERDAM, 

 LYONET, STRAUS and other writers already cited, C. SPRENGEL Commentarius de 

 partibus, quibus Insecta spirilum ducunt, Lipsise, 1815, 4to. cum tabulis; SUCKOW, 

 Respiration der Insecten, insbesondere uber die Darmrespiration der Aeschna grandis, 

 HEUSINGER'S Zeitsch. f. die organ. Physilc. n. 1828, s. 24 29 ; BURMEISTER ffandb. 

 der Entomol. I, s. 169 194 (a very careful revision of the observations of others and of 

 his own) and NEWPORT, Phil. Trans. 1856, Pt. 2, pp. 529 566 (or in TODD'S Cyclop. 

 II. pp. 982 990). We refer also to the beautiful figures in LYONET Traite an. de la 

 Chenille, PI. xxi., and STRAUS Anat. des anim. artic. PI. 7, in order to give an idea of 

 the minute division of the air-tubes. MARCEL DE SERRES has figured the tracheae and 

 air-sacs in some Orthoptera (Truxalis, Mantis) in Mem. du Museum, IV. PI. 15, 16. 



2 Already in T 792 VAUGUELIN had made experiments on the respiration of Insecta 

 (Locusta viridissima). Comp. also G. R. TREVIRANUS, Versuche uber das Athemholen 

 derniedern Thiere, Zeilschr. f. Physiol. iv. 183 r, s. 139, and NEWPORT, Phil. Trans, 

 1. 1., for the specific warmth, which was formerly denied by J. DAVY, against whose 

 observations NOBILI and MELLONI had already advanced objections (Ann. de Chim. et 

 de Physique, 1831, Octobre, pp. 207 210). All animals, LIEBIG 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 Icaltblutigc Ihiere, Gb'ttingen, 1825, s. 35, 36, 



