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IN VERTEBRA TE ZOOLOG Y 



sucker to some object, then drawing the body into a loop and 

 fixing the posterior sucker near the same spot. 



Shght development of the coelom and the dorsoventral flat- 

 tening of the body give leeches a distinct flatworm appearance. 

 Segmentation, presence of a coelom, development of a chtellum, 



Fig. 79. — Organization of a leech, Placobdella parasitica. I-XXVII, somites; 

 phg, pharyngeal glands; oe, esophagus; s, atrium or spermatophore sac; v.s, 

 seminal vesicle; t, testes; ov, ovary. C Redrawn from Whitman in Ward and 

 Whipple's Fresh-water Biology and reprinted by permission of John Wiley and Sons, 

 Inc.) . 



presence of a distinctly annelid type of nervous system, and 

 general organization, however, demonstrate close relationships 

 with the Oligochaeta. Michaelsen proposes a group Clitellata 

 to include the Oligochaeta and Hirudinea as two coordinate 



