GENERAL ZOOLOGY 



Pharynx 



Ovary 



Caeca 



(full) 



Caeca 

 (empty) 



Stomach 



Anterior sucker 

 Brain 



Circumpharyngeal 

 connective 



Segmental ganglion 



Penis 



Vagina 



Nerve cord 

 Ductus deferens 



Testes 

 Nephridia 



Rectum 



Intestine 



Posterior sucker 



Fig. 14.19. Class Hirudinea. 

 Dorsal view of the medicinal leech, 

 HiTudo medianalis, showing the gen- 

 eral arrangement of internal or- 

 gans. (Redrawn, after Parker and 

 Haswell, from F. A. Brown, Jr., in 

 F. A. Brown, Jr., et al.. Selected In- 

 vertebrate Types, copyright 1950 by 

 John Wiley and Sons, Inc., printed 

 by permission.) 



Larger coelomic spaces persist in connection with the segmental nephridia 

 and within the reproductive organs. 



Structurally, and to some extent functionally, the leeches show many 

 evidences of affinities with the oligochaetes. The indications are that the 

 two groups have evolved in different directions from common, or at least 

 similar, ancestry. 



Some fresh-water leeches are dangerous parasites of man and domestic 

 animals. Some large leeches have an estimated capacity of 8 milliliters of 

 blood. The terrestrial leeches found in many tropical countries of the Orient 

 are serious pests. They occur on or near the ground, in the dank vegetation 

 of the rain forests, and attach themselves to men and animals passing by. 



The Annelid Body Plan 



The type of structure found in annelids is important for comparison with 

 the plans of organization of simpler and of more complex metazoans. In such 

 comparative considerations the significant features of annelids involve chiefly 



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