ZOOLOGY FOR MEDICAL STUDENTS CHAP. 



by a si l.pment of longitudinally running muscles (Fig. 47, = 



these a, on the pair of mesenteries next the ciliated groove and 



.1 less conspicuous on those furthest removed from it. 



.,rc prolonged downwards beyond the truncated 



rn ,l ()t tlu- stomodaeum uml are then attached only by one the outer 



dy wall, the opposite margin projecting freely into the 



coel: 



Tries. 



end. 



FIG. 46. 



Alcycmium. Vertical section through part of colony, coel, Coelenteron ; end, endodermal tube 

 Bten "t I\\M neighbouring polyps; m.f, inosenterial ii lament ; m.f*, dorsal, uncoiled, 

 mocntrri il fil inn nt , nu-s, nn-v.Kloe.i ; sf>, spic.ulc ; st, stomodaeum. 



47, IJ). The free edge is thickened to form a con- 

 ioua thread the mesenterial filament (M.f). 



The rorlriurrir. caxity of the ])roje(liiig portion of the polyp is pro- 



tlnwnwanls into the substance of the colony, the mesenteries 



d downwards. In the case of the two mesenteries 



fnin the ciliated groove ("dorsal" mesenteries) the mesenterial 



-. is cuntinui'd right down into the basal part of the 



vcrcd with cells bearing powerful cilia which beat 



