ANNULOSA: ANNELIDA. 



26l 



The segmental organs of the Leeches differ further from those 

 of the other Annelida in not being in any way connected with 

 the process of reproduction. 



The nervous system consists of a prae-cesophageal ganglion, 



Fig. 128. A, Diagram of the Leech, showing the nervous system, and the ten eyes 

 placed on the top of the head. B, The leech dissected to show the alimentary canal 

 (i), and the " segmental organs," or so-called "respiratory sacs " (r r) ; as Anterior 

 sucker; ps Hinder sucker ; n n Nervous system; h Head, carrying the eye-spots. 



which gives branches to a number -of simple eyes, or ocelli, 

 which are placed on the head, and which is united by lateral 

 oesophageal cords to the ventral gangliated chain. The ven- 

 tral chain of the common Leech carries twenty-three succes- 

 sive pairs of ganglia, marking the composition of the body out 

 of the same number of segments or " zonites." 



The sexes are almost always united in the same individual, 



