INSECTA. 



979 



directly forwards in the middle line of the 

 body, and then backwards by the sides of the 

 thorax and abdomen, to the lateral and pos- 

 terior parts of the heart, into which it is re- 

 ceived, by means of transverse currents in each 

 segment, through the auricular space and ori- 

 fices. This course, as discovered by Carus, is 

 indicated in the description and diagram given 

 in a former part of this work.* The blood, 

 which is usually of a very transparent greenish 

 or yellowish colour, is filled with a great num- 

 ber of little particles, which were described by 

 Carus as oblong or oval, but more correctly 

 by Mr. Bowerbank f as flattened oat-shaped 

 masses, which retain their form while circu- 

 lating through the body, but like the particles 

 of blood in Vertebrata become globular imme- 

 diately they are brought into contact with water. 

 It is stated by Burmeister J that they vary in 

 diameter from" ^th to ,Lth of a line, but they 

 differ also in size in the same individual, and 

 are often rough or tuberculated as noticed by 

 dwards, and as distinctly seen in the blood of 

 Sphinx ligu!>t?-i. The motions of the blood, ren- 

 dered perceptible by the presence of these par- 

 ticles, was first observed by Carus in the aqua- 

 tic larva of Ephemera, in which, as in other 

 aquatic transparent bodied larvae, the particles 

 are very distinct. Baker|| and some of the older 

 observers in this country had long before seen 

 motions of the fluids in the limbs of some in- 

 sects, but Carus first discovered the existence 

 of a complete circulation. Carus saw the blood 

 distributed in several streams from the aortal 

 extremity of the dorsal vessel in the head re- 

 turning in currents, that entered the base of the 

 antennae and limbs, in which it formed loops, 

 and then flowing into the abdomen entered the 

 heart at its posterior extremity. Wagner^] con- 

 firmed Cams' discovery, and added some new 

 observations. He saw the blood flowing back- 

 wards in two venous currents, one at the sides 

 of the body and intestine, and the other along- 

 side of the dorsal vessel, and he discovered 

 that the blood not only entered at the ex- 

 tremity of the dorsal vessel, but also at the 

 sides in each segment, at the valves discovered 

 by Straus. Both Carus and Wagner, however, 

 believed that the currents of blood observed 

 by them were not inclosed in distinct parietes 

 or vessels. Mr. Bowerbank,** in repeating these 

 observations, saw also the blood distributed by 

 the dorsal vessel forming loops in the antennae 

 and limbs, and then passing backwards in la- 

 teral and transverse currents, enter at the valves 

 into the dorsal vessel. And he also observed 

 and clearly defined the structure and action of 

 the valves. He discovered, however, that the 

 currents of blood along the sides of the body 

 are really inclosed in distinct parietes, and 

 do not flow in the common abdominal cavity, 



* See Article CIRCULATION, vol. i. p. 652, fig. 

 325. 



t Entomol. Mag. vol. i. p. 244. 



j Op. cit. 404. 



$ Art. BLOOD, vol. i. p. 408. 



II On the Microscope, vol. i. p. 130. 



\ Isis, 1832. 



** Entomological Mag. vol. i. April, 1833, p. 239. 



as previously supposed, the boundaries of the 

 vessels inclosing these currents being clearly 

 definable. He has also expressed his belief 

 that a " much greater portion of the circulation 

 than we can clearly define is carried on within 

 given vessels, as the blood may frequently be 

 seen flowing in curved and other lines, and con- 

 fined within very narrow limits, but so deeply 

 seated amidst the muscles and intestines as to- 

 tally to prevent the boundaries of the current from 

 being clearly observed." We are ourselves most 

 distinctly of the same opinion, having formerly, 

 through the kindness of Mr. Bowerbank, been 

 allowed to examine the circulation in Ephemera 

 by means of his powerful microscope. W 7 e 

 believe also that we have seen distinct vessels 

 passing transversely across the dorsal surface of 

 each segment, in the direction of the anterior 

 part of each chamber of the dorsal vessel, 

 in the large pupae of Acherontla Atropos and 

 Sphinx iigustri* but whether these are vessels 

 returning to or distributed from each chamber, 

 as we are most inclined to believe, is not cer- 

 tain. If they be not vessels distributed from 

 the heart, it is a somewhat curious circumstance 

 that the whole of the blood should be first sent 

 to the head of the insect, and the viscera of 

 the abdominal region be nourished only by the 

 returning blood, which has in part passed the 

 round of the circulation. The only instance 

 in which vessels had previously been supposed 

 to be distributed directly from the heart in the 

 abdomen was pointed out so long ago as 1824 

 by Professor Muller,f who discovered a con- 

 nexion of the oviducts with the inferior surface 

 of the organ in many insects ; but these were 

 afterwards believed by Carus, Treviranus, 

 Wagner, and Burmeister to be only ligamen- 

 tous connexions. W 7 e have observed these con- 

 nexions in many insects, and certainly believed, 

 when we first noticed them, without being 

 aware that they had previously been seen by 

 Miiller, that they were vascular structures. We 

 have traced them, especially in the Carabidte, 

 into direct connexion with the or:an, but have 

 been unable to observe at what point the cavity 

 of the ovarial tubes commences, or where the 

 supposed ligamentous portion begins. We 

 have seen these connexions not only in the 

 perfect insects but also in the larvae, more espe- 

 cially in the males of Sphinx ligustri and 

 Odonestis potatoria. In these larvae the two 

 oblong testicles, not united into one mass as in 

 the perfect state, are each attached, side by 

 side, by two short filaments to that chamber of 

 the dorsal vessel which is situated in the ninth 

 segment. One of these attachments proceeds 

 from the anterior and the other from the pos- 

 terior part of each testicle. Now, if these at- 

 tachments be not distinct vessels, it is remark- 

 able that these glandular and secretory organs 

 should always be connected by mere ligaments 

 with the great circulatory organ, since, if the 

 object of their connexion were merely to retain 

 them in their place in the abdomen, it would 



* Dr. Roget's Bridgewater Treatise, vol. ii. 

 p. 245. 



t Nova Acta Nat. t. xii. 2. 



3s 2 



