Page:The Zoologist, 1st series, vol 1 (1843).djvu/120

92 lerably well seen without the aid of injection, on account of the dark red colour of the circulating fluid; and some of the smaller branches may be readily discerned by placing a leech, which has been kept for some time without food, in rectified spirit (alcohol), which coagulates the blood in the vessels, and at the same time preserves its red colour, as was, I believe, recommended and first practised by Dr. Kurzman.

a a. Lateral blood-vessels of the horse-leech. b. Dorsal vessel. c. Abdominal vessel. d. Portion of lateral vessel highly magnified. e. Muscular fibre of tunic. f. Muscular fibre of œsophagus. g. Blood-disks.

For our present purpose it will be merely necessary to consider the vascular system as composed of four longitudinal trunks, with their communicating branches. Of these four trunks two occupy the sides of the body, and from this circumstance they are termed the lateral vessels (fig. a a), whilst the remaining two are placed, one on the dorsal (fig. b), the other on the ventral surface (fig. c), in the median line of the body. These two last trunks communicate with each other by smaller branches, termed dorso-abdominal), which correspond with each segment of the body, and also with the lateral vessels, by a series of branches termed dorso-lateral. The two lateral vessels are considered to form the arterial portion of the system, while the dorsal and ventral vessels correspond to the venous. This distribution of the vessels may be readily understood by reference to the figure, where the arterial system is represented by the light vessels, the venous by the dark