X 



PHYLUM ANNULATA 



513 



The following diagram will serve to illustrate this view of the 

 relationships of the various groups referred to : 



Po ly c ha 



My i o sfomid<a 

 Sipunculoidea 



Echiurida 



Ol igoch jef a 



Hirudinea 



Archi-Annelida 



Hlstriobdellea 



Dinofihiiea RoHPera 



-Gastrofricha 



Trochojjhore 

 FIG. 426. Diagram illustrating the relationships of the Annulata and the Trochelmiiithes. 



It should be added, however, that it is not likely that the 

 trochophore actually represents the ancestral form, since, to some 

 extent at least, its special features, such as the special arrangement 

 of the cilia, may be adaptations to a pelagic mode of life. 



VOL. I. 



L L 



