^340. 



THE INSECTA. 



431 



CHAPTER VI. 



CIRCULATORY ORGANS. 



§340. 



The Circulatory System is feebly developed with Insecta, consisting of a 

 contractile, articulated Vas dorsale, and a cephalic Aorta. The first serves 

 as a heart, and the second is a simple conductor of the blood from the heart 

 into the body. In both of these vessels, the blood moves from behind forwards, 

 and, at its escape from the aorta, traverses the body in all directions, forming 

 regular currents which have, however, no vascular walls. In this way, it 

 penetrates the antemiae, the extremities, the wings, and the other appendages 

 of the body, by arterial currents, and is returned by those of a venous 

 nature. All the venous currents empty into two lateral ones running 

 towards the posterior extremity of the body, and which enter, through lat- 

 eral orihces, the dorsal vessel.* 



1 Swammerdamm, Malpighi, and others of the 

 ■older anatomists, had already formed a pretty exact 

 idea of the circulation of the luaecta. But, subse- 

 quently, it was entirely abandoned when it was ob- 

 served that the dorsal vessel was a closed tube, and 

 served only as a simple reservoir of the nutritive 

 juices. Carus was the first to demonstrate auew 

 the existence of a circulation which has since been 

 confirmed with all the three stages of insects. See 

 Carus, Entdeck, eines einfachen, vom Herzen aus 

 beschleunigt. Blutkreisl. in den Larven netzflüglioh. 

 Insekt. 1S27 ; Nov. Act. Acad. Nat. Cur. XV. 

 part II. p. 8, Taf. LI. ; and Lehrb. d. vergleich. 

 Zoot. 1834, p. 687 ; R. Wai^ner, Isis, 1832, p. 320, 

 778 ; Biirmeister, Ilandb. &c. I. p. 164, 436 ; 

 Bowerban/c, Entom. Mag. 1. 1833, p. 239, IV. 1835, 

 p. 179 (also in Froriep^s neue Notiz. XXXI.X. p. 

 149) ; Tyrrell, Philosoph. Trans. 1835, p. 317 ; 

 Newport, Cyclop. &c. II. p. 980 ; Milne Ed- 

 wards, Ann. d. Sc. Nat. III. 1845, p. 278 ; and 

 (^aatrefages, Instit. 1845, p. 305. This circula- 

 tion carried on by the dorsal vessel, having been 

 observed by so many distiugulslied naturalists, it is 

 truly incomprehensible that L. Diifour (Recherch. 

 sur les Hemipt. p. 272 ; Recherch. sur les Orthopt. 

 p. 287 ; Ann. d. Sc. Nat. XVI. 1841, p. 10 ; Mem. 

 presentes ä I'lnst. IX. p. 595, 601) can persist in 

 denying that the dorsal vessel is anything but a 

 secretory organ which, according to hhn, has no 

 opening and therefore nothing iu common with a 

 heart. He cites the authority of Cuvier who was 

 unwilling to accord to the f^as dorsale either the 

 name or the functions of a heart (Cuvier, Mi^m. 

 sur lamaniere dout se fait la nutrition dans les In- 

 sectes, in the Mem. d. 1. Soc. d'Hist. Nat. de Paris, 

 VII. 1798, p. 34, or ReiPs Arch. V. p. 97). L. 

 Diifour adduces, raireover, in support of his erro- 

 neous view, the following remark of Carus (Erläu- 



terungst. Hft. VI. p. 8), " In the perfect Insecta, 

 whose respiration is performed by a system of 

 tracheae traversing the entire body, the circulation 

 of blood would be useless." But to this it may be 

 replied, that Carus, by these words, has contra- 

 dicted his proper observations ; for he has shown 

 that there is a circulation in many perfect insects, 

 as is stated not only in the Nov. Act. Nat. Cur., loc. 

 cit., but also in the Erläuterungstafeln from which 

 the above citation was taken. At all events, the 

 proposition of Carus is correct, " that in insects, the 

 blood must come in contact with the atmospheric 

 air, which is accomplished by means of the tra- 

 cheau system." But this applies only to the small 

 portion of the circulation connected with the respi- 

 ratory process ; whereas, the larger portion, des- 

 tined for the general nutrition of the tissues, does 

 not evidently require the presence of tracheae. The 

 presence of a real blood-circulation by means of the 

 Fas dorsale, is so easily observed, that the injec- 

 tions of Blnnc/iard are scarcely necessary (Compt. 

 rend. XXIV. 1847, p. 870). 



If, in certain species, although transparent, these 

 phenomena are not observable, we must not be too 

 hasty iu denying its real existence, for the blood,- 

 which is not visible except through its globules, is 

 often so poor in these last, as to elude our observa- 

 tion, f^erloren has recently given a very com- 

 plete resume of what has been done on this sub- 

 ject, and has added new and confirmatory observa- 

 tions ; see Holländische Biitr. zu den anat. und. 

 physiol. Wissenschaft. I. Hft. 2, p. 220 ; and Me- 

 moire en response at la question suivante : tclaii'cir 

 par des observations nouvelles le phenomdne de la 

 circulation dans les lusectes, en recherchant si peut 

 la reconnattre dans les larves des differents ordres 

 de ces aniraaux, in the Mem. com'ouu. par I'Acad 

 de Belgique, XIX. 1847.* 



* [ § 340, note 1.] The results obtained by 

 Blanchard have been very satisfactorily conSrmed 

 by Agassiz (Proceed. Amer. Assoc. Advancem. Sc. 

 1849, p. 140, also its translation into French in the 

 Ann. d. Sc. Nat. 1851, XV. p. 358), who has suc- 

 ceeded in distinctly injecting the tracheae by the 

 dorsal vessel. These experiments I have had the 



good fortune to witness, and their character was 

 such as to leave with me no doubt as to the peri- 

 trachean circulation. See, also, the additional evi- 

 dence which Blanchard (Compt. rend. Oct. 6, 

 1851) has recently furnished of a peritrachean cir- 

 culation, which is very important and weighty. 

 He took advantage of the well-known fact that silk- 



