20 



the animul is foeding, the palottos ■■ >-" 'Ir-^vrr for.vards ar.d 

 tlie siphons are extended freely into the wat shown 



'g. 21. YAien it is disturbed ii. , ■^'^ siphons 

 are contracted very tmickly and the palettes forced into 

 the end of the tube us shov/n 



Mode of Btirro-.ving. - The manner of mechanical forpiation of 

 the burrow has been one of the most debated questions in 

 the natural history of the "^-Jiip-worms" and their allies. 

 In Teredo, various structures have had. this work assigned 

 to them, by various observers. In some cases tlie observ- 

 ers thought some chemical solvent to assist the mechanical 

 action by softening the wood. Hancock thought there were 

 siliceous particles in the mantle, to do the v/ork. He 

 probably observed the teeth as yet unattached to the shell. 

 Quatrefages thought it the "cephalic hood", aided by some 

 chemical solvent. This structure he described cs muscular, 

 though it is but little muscular and could do no such im- 

 portant work as he assigned to it. Jeffreys thought it 

 the foot, which by other observers v/as described as wholly 

 absent. Osier, in 1826, had suspected the real mode of 

 formation, though he did not actually observe it. The 



