Page:Popular Science Monthly Volume 8.djvu/698

678 Leeches are true parasites, although asking only food and taking care of themselves in the intervals of their meals. They suck the blood of their victim, and, when gorged to the very lips, fall off and perhaps for many weeks have no further need of assistance. The vampires of South America obtain support in a similar way, and are just as truly parasitic, although otherwise leading an independent life. The best-known leeches are those which prey on man and other mammals; but some are found which attack animals of still lower grade, especially the fishes. The organization of the leech appears always to be proportioned to that of the host which it frequents, the lower the grade of the latter the simpler the structure of the former. Those living on the mollusks are inferior to those found on fishes, and these again rank below the sorts that attack the mammalia. Fig. 8 (1, 2, 3, 4) shows the different appearances assumed by the skin after a leech-bite; Fig. 9 represents the structure of the jaws; and Fig. 10 is a longitudinal section of the body of the leech. The letters Fig. 8.