ACTINOZOA. 



145 



Two of these, the ' apical canals,' very short and 

 narrow, run directly downwards and outwards on 

 either side of the ctenocyst, and soon open exter- 

 nally as the ^ apical pores,' situate immediately 

 beyond the margin of the ' apical area.' Some 

 writers describe the apical canals as lateral, others 

 as antero-posterior in their direction. Both 

 opinions are partially correct, the apical pores 



Fig. 27. 



0' ^^ 7)1 



Morphology of PtEUEOBRACHiA : — a, diagrammatic longitu- 

 dinal section of Pleurobrachia ; b, the same in transverse section; 

 0, mouth ; S', digestiye cavity ; k', funnel ; 0', ganglion and 

 ctenocyst ; t', sac of the tentacle ; t, tentacle, with one of its 

 branches ; x* radial canal ; %') one of the ctenophoral canals ; x"> 

 apical canal ; X) paragastric canah The numerals i and 2 indicate 

 the first and second bifurcations of the radial canals. 



being obliquely opposite one another, though 

 placed on different sides of the body. Two other 

 canals, the * paragastric canals,' assume an upward 

 course, parallel to and not far from the flattened 

 sides of the digestive sac, but terminate caecally 

 before quite reaching its oral extremity. A third 

 pair of canals, much wider and shorter than those 

 just mentioned, radiate from the funnel in a 



