•^340. 



THE INSECTA. 



431 



CHAPTER VI. 



CIKCULATORY OKQANS. 



§ 340. 



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

 contractile, articulated Vas dorsale, and a cephalic Aoi'ta. 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 antennae, 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 orifices, the dorsal vessel.*^' 



1 Swammerdamm, Malpi^lii, and others of the 

 older anatomists, liad already formed a pretty exact 

 idea of the circulation of the Insecta. 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 anew 

 the existence of a circulation which has since been 

 confirmed with all the tliree stages of insects. See 

 Carus, Entdeck. eines einfachen, vom Ilerzen aus 

 beschleuni^t. Blutlcreisl. in den Larven netzfliiglich. 

 Insekt. 18J7 ; Nov. Act. Acad. Nat. Cur. XV. 

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

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

 778 ; Burmeiste.r, Handb. &c. I. p. 164, 436 ; 

 Bowerbank, Entom. Mag. 1. 1833, p. 239, IV. 1335, 

 p. 17'J (also in B'roriejt^s neuo Notiz. XXXIX. 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 

 Qtiatrefages, Instil. 1845, p. 305. This circula- 

 tion carried on by the dorsal vessel, having been 

 observed by so many distinguished naturalists, it is 

 truly incomprehensible that L. Dufour (Keoherch. 

 Bur les Hemijit. p. 272 ; Recherch. sur les Orthopt. 

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

 presentes d I'Inst. IX. p. 595, 601) can persist in 

 denying that the dorsal vessel is anything but a 

 secretary organ which, according to him, has no 

 opening and therefore nothing in conim;jn with a 

 heart. He cites the authority of Cuvier who was 

 unwilling to accord to the Kas dorsale either the 

 name or the functions of a heart (Cuvier, Mem. 

 sur la maniere dont se fait la nutrition dans les Iii- 

 sectes, in the Mem. d. 1. Sr>e. d'llist. Nat. de Paris, 

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

 Dufour adduces, moreover, in support of his erro- 

 neous view, the following remark of CarMS (Erlflu- 



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

 Blanchard have been very satisfactorily confirmed 

 by Agassiz (Proceed. Araer. 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 ejqjeriments I have had the 



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 bo 

 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 Erlauterungstafeln 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- 

 chean 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 

 f^as dorsale, is so easily ol)served, that the injec- 

 tions of Blanchard 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 in 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. Ferloren. 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 HoUaadische Beitr. zu den anat. und. 

 physiol. Wissensohaft. I. Hft. 2, p. 220 ; and M^- 

 maire en response i la question suivante : 6claircir 

 par des observations nouvelles le phenomine de la 

 circulation dans las Inseotes, en recherchant si peut 

 la reconnal:ro dans les larves des dilferents ordres 

 de ces animaux-, in the Mem. couronu. par I'Acad. 

 de Belgique, XIX. 1847.* 



good fortune to witness, and their character was 

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

 traohean 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 unportant and weighty. 

 He took advantage of the well-known fact that sill;- 



