Structure of Magelona. 4.51 



VII. The Tentacles. 



When the annelid is at rest amongst the sand it projects 

 its exti'emely elongated tentacles through the aperture of 

 its tube into the surrounding water, in which they are 

 jerked to and fro, stand stiffly out, or are gracefully curved 

 and moved in a serpentine manner here and there over the 

 sand — indeed, when many are confined in a vessel the organs 

 resemble independent worms. In large examples they measure, 

 when gently curved from the aperture in the sand, about an 

 inch and a half or two inches, and are capable of much greater 

 elongation. In the extended condition of the organs the 

 papillae are very prominent at the tip, projecting like a series 

 of pinnae along the inner or anterior border, and susceptible 

 of decided and independent movements. When the animal 

 lies in a free condition on the surface of the sand the tentacles 

 again are often beautifully coiled in a spiral manner or 

 perform various independent vermiform movements. During 

 the process of boring the tentacles are trailed behind and 

 flatly applied to the body, their most delicate region being 

 in the completed channel, while the stronger smooth part 

 only meets the slight pressure of the sand against which the 

 organs are thrust by the advancing snout. When reposing 

 within its tunnel the organs are stretched in a parallel con- 

 dition in front of it, ready to be protruded on the return of 

 the tide. 



Each tentacle forms a hollow contractile process, furnished 

 with a series of papillae along the anterior border. Ex- 

 ternally it is invested by the chitinous cuticle, which is 

 densest at the basal region on the smooth part of the organ. 

 On reaching the bases of the papillae this coat spreads over 

 them likewise, but is extremely attenuated toward the tip. 

 The subjacent hypodermic layer is largely developed, forming 

 at the base of the tentacle a considerable investment through- 

 out three-fourths of the circumference, while the remaining 

 anterior region is greatly thickened, thus foreshadowing the 

 special arrangement further outward. It is more finely 

 granular than the hypoderm of the body, shows the usual 

 fibrous or connective-tissue streaks, and likewise contains 

 the pigment. Proceeding outward, the thick anterior hy|)o- 

 dermic area by-and-by shows numerous low pale warts, which 

 soon attain a considerable size. In the living specimen each 

 papilla, in the somewhat contracted condition caused by 

 slight pressure, has a rather narrowed base, and is composed 

 of a continuation of the hypoderm and cuticle, as formerly 

 noticed. The central region is occupied by a series of 



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