394 



HIRUDINEA 



" Horsleches," said an old writer, " are wholesome to diawe 

 foorthe foule blood, if thei are put into a hollowe rede, and one 

 of their endes cutte of, whereby the blood maie run for the." But 

 it is clearly not easy for a creature destitute of jaws and teeth to 

 bite, and the similarity of general aspect has doubtless led to a 

 confusion with the savagely biting medicinal leech. 



The Hirudinea are all distinctly segmented animals, but the 



Fig. 202. Sense body of Macrobdella 

 sestertia. (After Whitman.) ep, 

 Epidermis ; s, clear cells. Highly 

 magnified. 



Fig. 203. Section through eye 

 of Haemadipsa japonica. 

 (After Whitman. ) ep, Epi- 

 dermis ; n, nerve. Highly 

 magnified. 



segmentation differs from that of the Oligochaeta in two points. 

 In the first place the number of segments is much smaller in a 

 leech than in an Oligochaete, although the difference does not 

 appear great at first sight. 



A leech's body may seem to be composed of seventy, eighty, 

 or one hundred segments, a number quite as great as is found, 

 for example, in the genus Perichaeta among the earthworms ; but 

 the apparent number of segments in the leech is produced by a 

 very marked annulation of the real segments ; and this is indeed 

 the second point of difference referred to above. But there 

 are earthworms which show frequently a secondary annulation, 

 secondary because it appears late and does not affect other organs 



