930 



INSECTA. 



probably be as well answered by an attachment to 

 any oilier part. These considerations certainly 

 lead us to hesitate to admit that they are mere 

 ligaments. Whatever be their nature, as MiiHer 

 has observed, their existence is indubitable. 



Besides the parts now described, there is 

 also another which is connected with and 

 forms part of the vascular system, but the ex- 

 istence even of which has hitherto been almost 

 overlooked. This is a distinct vascular canal, 

 which is extended along the upper surface of 

 the abdominal portion of the cerebro-spinal 

 cord in perfect Lepidopterous insects, and 

 which we have traced from the thorax to the 

 termination of the cor.d. We have designated 

 this structure the supra-spinal vessel. It is 

 placed immediately above the cord, and is 

 covered by transverse muscular fibres, which 

 exclude it from the common abdominal cavity, 

 and give to the whole cord, when removed from 

 the body and examined by transmitted light, 

 a flocculent appearance. This appearance was 

 first noticed by Lyonet,* but the vessel between 

 it and the cord was not detected by him. It 

 was subsequently figured and described by us 

 in the Sphinx^ and the whole of our recent 

 observations J have confirmed the opinion we 

 then entertained of it. It is a most distinct 

 structure in the abdomen of the Sphinx, and 

 may be readily seen after the abdominal cord 

 has been carefully removed from the body with 

 its surrounding structures and placed for some 

 time in spirits of wine. We believe this vessel 

 to be the chief means of returning the blood 

 from the middle and inferior portion of the 

 body to the posterior extremity of the dorsal 

 vessel or heart, and that it is analogous to a 

 structure which we have found to be a supra- 

 spinal vessel in the Scorpion and Centipede, 

 that had previously been supposed to be a 

 loose and easily detached portion of the nervous 

 system, but which is now proved to belong not 

 to the nervous but to the vascular structures. 

 We are strongly inclined to suspect that this 

 supra-spinal vessel in insects is connected with 

 the anterior portion of the dorsal vessel or 

 aorta, in a manner similar to the connexion 

 which was shown by Mr. Lord || to exist be- 

 tween the corresponding structure and the heart 

 in Myriapoda. (SeeMvniAPODA.) We believe 

 also that we have seen a corresponding vessel iii 

 the larva of the Sphinx, but of so delicate a struc- 

 ture as almost always to elude detection. It will 

 thus be seen that the blood certainly flows in 

 distinct vessels, at least in some parts of the 

 body in perfect insects, and that vessels exist 

 even in the larva. But although a circulation 

 of the blood has been seen by Carus, Wagner, 

 and others in many perfect insects, it has been 

 shown only in the appendages of the body, and 

 in those chiefly in recently developed specimens, 

 while it has been supposed to move only in in- 



* Recherches sur 1'Anat. et Ics Metam. de diffe- 

 rcntes Especes d'Insectes. Paris, 1832, p. 505 

 pi. Iii. fig. 18. and pi. liv. fig. 2. 



t Phil.Trans.p. ii. 1834, p.395, pi. xiv. fi?.9(a) 



t Medical Gazette, March 17, 1838. D 973 



$ Id. March 17, 1838, p. 971. 



|| Id. March 3, 1838, p. 893. 



tercel lular spaces and not in distinct vessels. 

 This opinion, however, is now invalidated by 

 our discovery of a supra-spinal or great ventral 

 vessel. A motion of the fluids has been seen 

 by Cams in the wings of recently developed 

 Libellulida:, Ephemera lutea, and E. niargi- 

 natUj and Clirysopa perla; among the Coleop- 

 tera in the elytra and wings of La/npi/ris italica 

 and L. splendidula, Melotonlha solstitialtt', and 

 Dyticus. But Carus was unable to detect it 

 in the wings of Orthoptera, although, accord- 

 ing to Humboldt,* Ehrenberg has seen it in a 

 species of Mantis, and Wagner in the young 

 of Nepa cinerea and Cimex lectuiarius among 

 the Hemiptera; but it has not yet been ob- 

 served in the Hymenoptera. Burmeister has 

 seen it in Eristalis tenax and E. nemorum 

 among the Diptera, and Mr. Tyrrelf in M-uaca 

 domestica as well also as in Geophilus and Li- 

 tlwbius forjicatus in the Class Myriapoda. In 

 addition to these Mr. Bowerbank has seen it in 

 one of the Noctuida; Phlogophora wcticu- 

 losa^ in the Order Lepidoptera, in which it 

 was seen also in the rodimental wings of some 

 pupae by Carus. Some of the most interesting 

 observations that have yet been made upon 

 the motions of the blood in these organs are 

 those of Mr. Bowerbank in Clirysopa perla. 

 Mr. Bowerbank found that in the lower wing 

 of this insect the blood passes from the base 

 of the wing along the costal, post-costal, and 

 externo-medial nervures, outwards to the apex 

 of the organ, giving off smaller currents in its 

 course, arid that it returns along the anal or 

 inferior nervure to the thorax. He states that 

 the blood occupies the chief part of the cavi- 

 ties of these nervures, in each of the largest of 

 which is a very small trachea. From this 

 statement it has been rather hastily concluded 

 that the nervures of the wings are only venous 

 trunks, or passages for the circulatory fluids, 

 and are not formed, as hitherto supposed, 

 chiefly by ramifications of the tracheae. He 

 found tracheae existing in the larger of these 

 cavities, which measured only 22 y.h of an inch 

 in diameter, while the cavities themselves mea- 

 sured ? i g of an inch ; but in others the tracheae 

 measured ig ' in th, while the cavity measured only 

 sqgth. He states also that the tracheae very rarely 

 give off branches while passing along the main 

 nervures, and that they lie along the canals in 

 a tortuous direction. In consequence of these 

 most interesting observations we have examined 

 the wings of some dried specimens of this in- 

 sect, and have found that there exists, as Mr. 

 Bowerbank remarks, a very large and perfectly 

 transparent space around the tracheae, which is 

 more or less distinct in different specimens, but 

 in a few instances is not observable. But we have 

 invariably found that the tracheae not only exist 

 throughout the whole of the ramifications of the 

 wings, but also give off branches at every ner- 

 vure or space along which the fluid passes. 



* Burmeister's Manual, p. 408. 



t Proceedings of the Royal Society, Jan. 15, 



} Entomological Magazine, vol. i. April, 1833, 

 p. 243. 



$ Op. cit. vol. iv. Oct. 1836, p. 179, pi. xv. 



