678 



THE POPULAR SCIENCE MONTHLY 



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 moUusks 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 



a- 



2 



Fig. 8. 



E- 



m^='l . 



7-1 



Fio. 10. 



h~i 



Fio. 8. Different Forms of the Bite of a Leech. 

 Fig. 9. 1. Sucker, open ; a. Jaws. 2. One op the Jaws m.\gnipied. 



Fig. 10. Section op a Leech: a. Anterior Sucker; 6, Posterior buclier; r, Anns ; d, Stomach ; 

 ce, CEsophagus; i, Intestine; s s. Glands of the Skin. 



