130 Natural History Bulletin. 



distinguish empty calicles from primary canals. Tiie large 

 space in the upper part of fig. 4, PL III, for instance, is prob- 

 ably a longitudinal section of a calicle, and the two large 

 spaces below may be sections cut toward one side of the cali- 

 cle. How this may come about can be readily seen by a 

 reference to fig. 5, PI. Ill, which is part of a longitudinal sec- 

 tion of a branch. If a section were cut at right angles to the 

 plane of the paper and the axis cylinder, so that the section 

 would traverse the large opening between the calicle on the 

 right and the primary canal (f, f), the line of demarkation be- 

 tween calicular cavity and canal would not be apparent m 

 the section. The connection between the two is so broad in 

 this species that some of the calicles appear to be almost bot- 

 tomless so far as single sections will show. 



However much these canals may differ in size they are all 

 grouped around the axis cylinder and are strictly homologous 

 with the primary water-vascular canals as described in Plex- 

 aurella dichotoma. They are lined with a well defined endo- 

 thelial layer which is plainly seen to be continuous with the 

 endothehal calicular lining (fig. 5, d, d). The individual cells 

 of this lining are quadrate in form and have large granular 

 nuclei (fig. 8, d). Observations were not made upon living 

 specimens to ascertain whether these cells were furnished with 

 cilia or not, neither can cilia be discerned in sections of alcoholic 

 specimens. It is reasonable to suppose, however, that they 

 exist, having been demonstrated in many allied forms. 



When the endothelial lining is viewed from above, and not 

 in section, it presents a surface much like that of mucous 

 membrane from the higher vertebrates. 



The Secondary Water-vascidar canals offer no characters 

 by which they may be distinguished from those of other spe- 

 cies already described. Their number, however, is less than 

 in Brtareum. The cells with which they are lined differ in no 

 important particular from those of the primary canals. Being 

 simply continuations of the latter, the lining of these canals is 

 of course endothelial. The gastro-vascular cavity of the 



