264 



EMBRYOLOGY OF TEREBRATULINA. 



EXPLAN'ATIOX OF LETTEIIS ACCOMPANYING THE FIGURES. 



ni, mouth. 



ce, cesophagus. 



s, stomach. 



t, tentacles or cim. 



a, alimentary tract. 



pi, pallial cavity. 



pv, perivisceral cavity. 



pc, peduncular cavity. 



c, cephalic segment. 



th, thoracic segment, 



p, peduncular or caudal segment. 



h, head. 



ap, anterior parietal wall and head. 



e, area of embryonic shell. 



/, fold of larger, or ventral area. 



pr, primary coeca. 



ds, deciduous setae. 



es, embryonic shell. 



X, foreign particles adhering to peduncle. 



