Licence: Public Domain Mark
Credit: Circulation / by Allen Thomson. Source: Wellcome Collection.
Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.
18/52 page 16
![ries ; by the branchial veins it gains the lower vessel. This vessel may be regarded as the systemic artery, and sends the arterial blood, by the numerous anastomosing branches, uj)- wards across the intestine, and through the other parts into the upper vessel. The upper vessel communicates also with the lower ante- riorly by the lateral dilatations named auricles, which are supposed to furnish some blood to the upper vessel. A part of the blood at the anterior extremity of the lower vessel is said to be propelled into the two subordinate vessels placed along the sides of the nervous cord. In this course which the blood is stated to follow, it does not appear to be known whether its motion is of a regular progressive kind or only undulatory. Leech.—In the leech the principal and most highly contractile longitudinal vessels are placed one on each side (jig. 13, a, a), and there are also two lesser longitu- dinal vessels, one supe- rior and the other inferior (a*), all which commu- nicate freely together by small cross branches along the whole body (c). It is remarkable that the lower median vessel (a*) incloses the ganglionic nervous cord, so as to bathe it with blood. Both pulmonary arteries and veins are branches of the lateral ves- sels ; a capillary network between them distributing the blood minutely over the pulmonary sacs or vesicles. The pulmonary veins form very remarkable dilated and coiled por- tions, which seem to be endowed with a high de- gree of contractility. Ac- cording to J. Muller, for a certain number of pul- sations, the middle and the lateral vessel of one side contract together, and pro- pel the blood into the lateral vessel on the other side, and then the order is reversed, and the middle vessel acts along with the lateral vessel of the other side, so that one lateral vessel is always dilated while the median and opposite lateral ones are contracted, and vice versa. According to some there is thus only an alternate motion of the blood from one side to the other, while others believe that there is at the same time a gradual progressive motion of the blood for- wards in the upper vessel and backwards in the lower one.* The course of the blood in the ])rincipal * See a full account of most of the opinions of observers on this subject, as well as original obser- vations by Rudolf Wagner, in the Isis for 1832, p. 643. ' parts of the circulatory organs is nearly the same in the rest of the Articulata, viz. Crustacea, Arachnida, and Insects, as in Annelida. In all of them the central propelling organ, whether in the form of a heart or consisting only of a dilated arterial vessel, such as the dorsal vessel of in- sects, is situated on the upper surface of the” animal, above the alimentary canal, while the returning vessels are situated on the lower sur- face of the body, on each side of the nervous ganglionic cord. The respiratory circulation, when occurring in a distinct set of vessels, forms a part of the venous system, and the heart, which has no auricle, is systemic or aortic. Insects.—All perfect Insects, whether inha- bitants of air or water, breathe air alone. In these animals there is not a separate and dis- tinct respiratory organ in one part of the body only, but the atmospheric air is carried by minute elastic and tough tubes ramified to an infinite degree of minuteness into every part of their body. The dorsal vessel of insects forms a long and wide contractile artery, larger in general behind than before, in which the contractions begin at the posterior extremity, and proceed gradually forwards with an undulatory motion. In the greater number of perfect insects, w’e are not acquainted with any other vessels or passages in the body, through which the blood moves, and this fluid seems in these insects to oscillate backwards and forwards in the dorsal vessel alone. This state of the circulation in insects, according to the ingenious views of Cuvier, is related to the distribution of the respiratory organ over the whole body, in consequence of which the air is brought in contact with the more perfect blood contained in the dorsal vessel, and the nutritious fluids supposed to pervade interstitially the rest of the body. The recent discovery by Cams of a continuous cir- culation of the blood through arteries and veins in a few of the perfect insects, and more espe- cially in some larvae, must modify the above views, which, ingenious as they must appear to all, do not account so satisfactorily for the ab- sence of a systemic as for the want of a pulmo- nary circulation. The circulation of the blood of Insects may be most easily seen in the aquatic larvae of Neuropterous Insects, as the Agrion, Ephemera, Semblis, and Libellula,* in which it was first discovered. In these larvae it may be described generally as follows. The dorsal vessel (Jig. 14, H) is connected anteriorly and posteriorly by several branches with the inferior or returning vessels ‘I {v, v), which, running along the whole body, receive the blood from the anterior extremity, and carry it into the posterior extremity of the dorsal vessel. The antennae and first joint of the legs, as well as the fin-shaped caudal pro- cesses, receive each a loop of vessel from the abdominal current; and from the motion of the globules in these transparent parts, the circula- tion can be more easily seen in them than in * We have ourselves seen the circulation in the larvae of two Neuropterous Insects. Fig. 13.](https://iiif.wellcomecollection.org/image/b22468390_0020.jp2/full/800%2C/0/default.jpg)
No text description is available for this image
No text description is available for this image
No text description is available for this image