No. 3.] GROWTH AND METAMORPHOSIS OF TORN ARIA. 449 



REFERENCE LETTERS. 



A. 



ac. 



b, b'. 



be*. 



be 3 . 



cb>. 



d. v. 



e. 



g 



g-P- 



g r - 



h. 



I. 



I. 



t. 



Lb. 



m. b. 



o. 



P- 

 pc. 



<}• 

 S. 



v. 



V. V. 



w. 



w.p. 



x. 



Apical plate. 



Anterior lateral fold. 



Upper turn of longitudinal band. 



Second (paired) body cavities. 



Third (paired) body cavities. 



Circular ciliated band. 



Dorsal blood-vessel. 



Anterior enteroccel. 



Posterior collar groove. 



Second gill pouch. 



Groove at union of oesophagus and stomach. 



Heart or proboscis blood-vessel. 



Intestine. 



Lower limb of longitudinal band. 



Part of longitudinal band joining /. 



Longitudinal band. 



Mouth. 



Ciliated circumoral region below mouth. 



Muscle band from apical plate to enteroccel. 



Anus. 



Notochord. 



CEsophagus. 



Pre-oral part of longitudinal ciliated band. 



Post-oral part of longitudinal ciliated band. 



Posterior lateral fold. 



Upper wave of lower limb of longitudinal band. 



Stomach. 



Proboscis vesicle = " heart." 



Ventral blood-vessel. 



Digestive tract wall. 



External opening of ant. enteroccel = water pore. 



Posterior lateral area. 



Middle lateral area. 



Anterior lateral area. 



