PHYLUM ANNULATA 



483 



In adult structure, particularly in the absence of parapodia and 

 setae and of a coelome, the Hirudinea diverge somewhat widely 

 from the Chaetopoda ; but a study of their earlier developmental 

 stages shows unmistakably their close connection with the latter 

 group, more particularly with the Oligochseta. 



The following diagram will serve to illustrate this view of the 

 relationships of the various groups referred to : 



Polychaeha 



Myzosfomida 

 Gefshyr 



Oligochaefa 



Hirudinea 



Arch i -Annelida 



Dinofihilea 



Gasfrc^richa 



Trocho(ohore 



FIG. 385 Diagram illustrating the relationships of the Annulata and the Trochcliuinth 



I I 2 



