SANGUIFEROUS SYSTEM. 449 



abdomen. The heart, still destitute of auricle, is attached, 

 as in other entomoid classes, to the upper and lateral parts of 

 the segments, by muscular bands extending from the sides of 

 each cavity ; these muscular bands have a triangular form, 

 tapering as they proceed laterally to the segments, and they 

 leave narrow openings between their broad insertions into 

 the tendinous, investing pericardium, to admit the lateral 

 abdominal currents. From this median dorsal abdominal 

 heart, the thoracic aorta is continued forwards, with thin 

 membranous parietes, and without sending off branches, 

 to the head where it has been shown by Carus to divide into 

 several lateral currents (133 D. c. d.), but the parietes of the 

 aorta are not perceptibly continued onwards around these 

 currents so as to confine them within distinct vascular canals. 

 The current of blood-globules from the anterior part of the 

 aorta is observed to divide into numerous distinct arches 

 (133 D. c. d.) which radiate upwards, laterally and backwards, 

 sending off similar isolated currents to the antennae and other 

 parts of the head, but there is no appearance of vascular 

 ramifications or capillary vessels in the sanguiferous system of 

 insects, which we observe so remarkably developed on their 

 respiratory organs, and which are obvious in the circulating 

 vessels even of the lower annelides. 



The currents of blood, forming arches or loops in the 

 head and its appendices, reunite and terminate in the 

 two great lateral inferior returning veins which, in their 

 course backwards, give off similar small currents to the 

 legs and the wings. A single stream is observed to 

 enter the anterior part of the haunch in each of the legs, 

 (133. D./. /*.) and to flow, on the same side, towards . the 

 tarsi, but to a variable distance in different insects; the 

 current returns on the opposite part of the leg, to the haunch, 

 and re-enters the great abdominal vein of that side, so that a 

 single loop sometimes reaching to the tarsus, is thus formed 

 by the current in each leg. The blood, however, is more ex- 

 tensively distributed over the wings, especially in the soft 

 and pliant condition of these parts, when first escaped from 

 the larva covering or the chrysalis state. Although the course 

 which the blood follows in traversing the wings of insects, 

 is very different in different species, and varies according to 

 the form, structure, and reticulations of these organs, it is 



PART V. G G 



