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MUSEUM OF COMPARATIVE ZOÖLOGY. 107 
iymnolaemata) 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 œsophagus 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 thiekenings 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 Phylactole- 
mata or “ Diaphragma ” of Gymnolemata (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 cyticularized. It is not so completely closed as to pre- 
vent communication between the colomata of the two individuals it 
separates. 
The mesodermal cells of Paludicella become stored with food mate- 
