THE CTENOPHORA 



terminology (9), the plane in which the stomodaeum is compressed 

 will be called the sagittal, that in which the infundibulum is com- 

 pressed the transverse plane. As the tentacles lie at either end of 

 the transverse plane, the latter is sometimes called the tentacular 

 plane. 



As the whole plan of the Ctenophoran body is dominated by 

 these two planes lying at right angles to one another, it will be 

 convenient to refer the position of other organs to them. Accord- 



-c.tr: 



c.ss. 



Fio. I. All the figures are of Pleurobrachia pikus. 



1. The animal has been cut in half vertically rather to one side of the transverse plane 

 st, stomodaeum ; i, infundibulum ; ic, infundibular canal ; sic, stomodfeal canals ; trc, transverse 

 canal, on which are seen the cut ends of the secondary canals ; tb, tentacle base ; tsh, tentacle 

 sheath. 



2. The animal has been similarly cut in half in the sagittal plane, a, sub-sensory am- 

 pullae ; iiw:, meridional canals ; ssc, sub-sagittal and, str, sub-transverse gastrovascular canals. 



3. View of the gastrovascular system in an animal cut across just above the level of the 

 infundibulum. Lettering as before. 



4. View of the aboral aspect of Pleurobrachia showing the central otolith mass, the polar 

 fields, 1'f; the four ampullae and two excretory openings, the eight ciliated furrows, the 

 costae and the fringed tentacles ; ess, sub-sagittal and, ctr, sub-transverse costae. 



5. Diagram illustrating the symmetry of a cydippiform Ctenophore. SS, sagittal axis ; TT, 

 trans'verse axis ; ssa, sub-sagittal radii ; tra, sub-transverse radii. 



ingly, organs which are adjacent to the sagittal plane will be 

 called sub-sagittal, those which are adjacent to the transverse plane 

 will be called sub-transverse. 



The infundibulum is lined by endoderm, and is the true 



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