MUSEUM OF COMPAEATIVE ZOOLOGY. 107 



Gymnoleemata) the mouth of the invagination pocket rapidly closes to 

 give rise to the neck of the polypide (page 56). In the latter case, the 

 cavity of the bud arises only secondarily by a separation of its walls 

 (page 18). 



By a rapid growth of the walls of the bud, its distal part, in which the 

 alimentary tract is to arise, is formed. Since this rapid growth occurs 

 earlier at the anal side than at the oral, the rectum is formed first, the 

 stomach last (pages 19, 57). 



By an approximation of the lateral walls, alimentary tract and atrio- 

 pharyngeal cavity become separated. 



The oesophagus arises as a pocket of the atrio-pharyngeal cavity, and 

 secondarily unites with the stomach (pages 19, 58). 



The lophophore arises first as two lateral thickenings of the atrio- 

 pharyngeal wall, then as two lateral folds, whose cavity becomes the ring 

 canal (pages 20, 58), 



Tentacles appear on the ridge of the lophophoric fold thus established, 

 and like it are formed first at the sides of the polypide, then anteriorly 

 and posteriorly (pages 22, 59). 



The posterior end of the lophophoric ridge is the last to be formed, 

 and, in forming, it cuts off the anal part of the atrium from the inter- 

 tentacular cavity (pages 23, 62). 



The compressed intertentacular cavity becomes circular by change in 

 position of the oral tentacles (pages 24, 62). 



The ganglion arises as a depression in the floor of the intertentacular 

 room, and becomes included in the pharynx, which is differentiated by 

 the change in position of the oral tentacles (pages 26, 61). 



Muscles and funiculi arise from the coelomic epithelium of both the 

 body wall and the bud (pages 27-31, 63). 



The neck of the polypide may sink to a considerable distance below 

 the general level of the body forming the ''Randwulst" of Phylactolse- 

 mata or " Diaphragma " of Gymnolaemata (pages 31, 63, 103). 



The atrial opening first arises at a late period by separation of the 

 cells of the neck. 



The communication plate arises in Paludicella as a circular fold 

 of the layers of the body wall, the mesodermal cells at the centre of 

 which become cuticularized. It is not so completely closed as to pre- 

 vent communication between the coelomata of the two individuals it 

 separates. 



The mesodermal cells of Paludicella become stored with food mate- 



