PHYLUM AXNULATA 



513 



The following diagram will serve to illustrate this view of the 

 relationships of the various groups referred to : 



Poly c ha efa 



Myzosfomida 



Sipunculoidea 



Echiurida 



Hirudinea 



Archi -Annelida 



Hlstriobdellea 



Dinojahiiea Roh'fera 



-GasfroCricha 



Trochophore 

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



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 



