98 



E. PERCIVAL 



as undifferentiated and, in the cases where polyps are produced, 

 they have remained so. It is interesting to note how they 

 agree in general behaviour with the upper part of the base of 

 the strobila, which produces oral disc and tentacles, while the 

 segment above gives rise to an ephyra. 



The several ways in which a polyp may be formed are thus : 



By direct development from the egg. 



By the outgrowth of stolons from a polyp. 



By the elaboration of the basal portion of a strobila. 



By the separation of an unchanged oral disc. 



By the elaboration of an intermediate segment. 



I wish here to acknowledge my indebtedness to Professor 

 W. Garstang for the kindly criticism and help which, from time 

 to time, he has afforded. 



Summary. 



The manubrium of a primarily non-terminal ephyra is formed 

 from the connecting tube between two ephyra rudiments. 



The proboscis of the polyp remaining arises in a manner 

 similar to that of the manubrium of the non-terminal ephyra. 



The apical opening of an ephyra normally closes before 

 liberation. 



The connecting strands are covered with endoderm. ^ 



The longitudinal muscles of a polyp may be hollow and the 

 cavities are not in communication with the peristomial pits. 



The formation of the peristomial pit is associated with the 

 development of the manubrium. 



The gastral filaments are formed as paired outgrowths of the 

 endoderm of the columella. They do not involve the longitu- 

 dinal muscle in their production. They originate early in the 

 history of an ephyra. 



There are definite currents over the ectoderm caused by 

 flagellated ectoderm cells. 



The segments of a strobila may give rise to ephyrae or polyps 

 and the oral disc may separate unchanged to continue its 

 existence as a polyp. 



