Galloway — Dero vaga. 



PLATE 3. 



Fig. 15. Sagittal section showing development of the ventral nerve chain in the 

 preanal zone of a recently separated zooid. X 312. 



Fig. 16. Parasagittal section, considerably to one side of median plane ; stage 

 about the same as that represented in Fig. 9. X 218. 



Fig. 17. Similar section, later stage. X 375. 



