234 



CCELENTERATA 



organs, and which must be regarded r.s transverse rows of long agglutinated 

 cilia. The combs (tig. 2oyA) arise from thick epithelial ridges, transverse 

 to the meridional bands, and are so far apart that the free edges of one 

 comb overlap the base of the next like shingles. In consequence of their 

 fibrous structure the combs are strongly iridescent and in motion cause a 

 beautiful play of metallic red, blue, and green over the meridional bands 

 These combs act like oars and row the body about. Since the combs 

 begin some distance from the aboral pole, they are connected with it by 

 means of ciliated grooves following the line of the meridional bands. 

 Experiment shows that the sense body is an organ of equilibration and for 

 correlating the action of the different rows of combs. 



The ectoderm gives origin to two other important organs, two pole fields 

 and two tentacles. The pole fields (fig. 209, pp) are two epithelial patches 

 extending a short distance in the sagittal axis from the sense body and 

 possibly are olfactory or taste organs. The tentacles arise, in the trans- 

 verse axis, from the bottom of deep tentacular sacs (fig. 207, f-) from which 

 they project as long cords with numerous lateral branches, and into which 

 they may be retracted. Tentacles and branches contain an axial muscle, 

 while the ectodermal coating consists largely of adhesive cells. These are 

 spherical bodies (fig. 210) covered with a very sticky granular secretion, 

 and, like a Vorticella, supported on the end of a spiral 

 stalk muscle. These are used in capturing prey, which 

 adheres to them and is drawn inward by the muscles. 



The ectoderm also forms part of the gastrovascular 

 system. It turns inward at the mouth situated at 

 the lower end of the chief axis and lines the large 

 space commonly called stomach (fig. 207, /), but which 

 corresponds to the oesophagus of the Actinozoa. At 

 the aboral end of this stomach begin the true ento- 

 dermal portions, the so-called funnels, and from them 

 run canals distributed through the jelly to the various 

 organs. Two (rarely four) funnel canals run to the 

 aboral pole and empty (fig. 209, to) near the sense body; 

 a second pair, the paragastric canals (fig. 207, mg), 

 which run parallel to the oesophagus, end blindly. The perradial canals 

 (g) proceed outward from the funnel, and besides giving off a canal to the 

 base of the tentacle, each divides dichotomously Twice, first into interradial 

 and then into adradial canals, each of these last connecting with a meridio- 

 nal vessel running just beneath a row of combs, nourishing them as well 

 as the gonads. The gonads consist of two bands, one male, the other 

 female, running in that wall of the meridional vessel nearest to the combs 



FIG. 210. Ad- 

 hesive cells of 

 Ctenophora (after 

 Samassa). 



