SEA-MA T MAKERS. 295; 



tentacles when expanded form a bell-shaped wreath, 

 and are slender hollow filaments, with a line of movable 

 cilia down two opposite sides, which, by their inces- 

 sant motion, cause an inward current of the water, 

 and sweep the floating particles of 

 food into the mouth at the centre. 

 In number the tentacles vary from 

 eight to eighty, and are very ener- 

 getic in their movements. They 

 are probably the sole organs of 

 touch which the animals possess. 



The sheath is a membraneous 

 extension, from the upper extremity 

 of the polype cell, to the base of 

 the crown of tentacles, when ex- 

 panded, and when the tentacles are 

 drawn in the sheath is drawn in 

 with them. " The invagination of 

 the sheath is due to its attachment, FIG. 57. 



at its upper extremity, round the BRANCHED TUBULAR 



7 ' POLYZOA 



base of the crown of tentacles ; (Fredericella\ 

 as the latter descends, in obedi- 

 ence to the summons of the retractor muscles, it Is>. 

 of course, drawn down with it, and reversed as< 

 the finger of a glove might be under similar circum- 

 stances, forming a protective case around it, which 

 sometimes exceeds it in length. By this arrange- 

 ment the cell (Zocscium] is completely closed ; there 



