Galloway. — Dero vaga. 



PLATE 5. 



Fig. 24. Only the margin of the prostomium of posterior zobid appears in this sec- 

 tion, which is three sections anterior to that of Fig. 23. The ventral 

 part of the section passes through the undifferentiated segment-form- 

 ing zone of the anterior individual. (Compare Fig. 15, Plate 3, which 

 represents a more advanced stage in longitudinal section.) 



Fig. 25. Frontal section through stage of about the same age as that shown in 

 Fig. 16, Plate 3. X 218. 



Fig. 26. Frontal section through head of posterior zouid which has been separated 

 from the anterior zooid two hours. X 166. 



Fig. 27. Section of same series, four sections ventral to the preceding. The lateral 

 grooves of the mouth are shown (i'vag. os. I.). X 166. 



Fig. 28. Parasagittal section, nearly median, through the head of a posterior 

 zooid, showing distribution of muscles. Ventral nerve cord is not 

 shown. X 166. 



Fig. 29. Parasagittal, but more lateral, section from the same series. X 166. 





