354 ROXIE A WEBER. 



EXPLANATION OF PLATE III. 



Helodrilus caliginosus trapezoides. 



16. No. i viewed from the side of the mouth opening. 



17. A section through No. i horizontal to the mouth opening, showing the 

 cerebral ganglia on one side of the pharynx and the cord tissue on the opposite 

 side. 



1 8. No. 67, united through two segments. 



19. A transverse section through the posterior part of the united portion show- 

 ing the cerebral ganglia joined to the ventral ganglia (vg) by commissures. 



20. A section through a gastrula stage showing bud formation. 



