TEREDO. 125 



hinge at a right angle. The shell eovers and protects 

 the mouth, palps, liver, and other delicate organs. The 

 body tapers gradually to the outer or nearer end, where 

 it becomes quite small and attenuated ; it contains the 

 gullet, intestine, and gills, and is enveloped in a thin 

 membrane or mantle, which forms at the outward point 

 two cylindrical tubes, mostly of unequal length. The 

 larger tube takes in infusoria or similar animalcules, 

 which constitute the food of the Teredo, as well as im- 

 bibes water charged with air for the purpose of respira- 

 tion and keeping the whole fabric moist; while the 

 smaller tube is employed in the ejection of the water 

 which has been exhausted or deprived of its aeriferous 

 qualities, and also serves to get rid of the woody pulp that 

 is excavated bv the Teredo. Both tubes form a kind of 

 hydraulic machine. At the base of each lies one of the 

 paddles, often termed " pallets/' and which may be 

 translated into scientific language as " claustra."" When 

 the Teredo is alarmed, or not feeding, it withdraws its 

 tubes into the neck of its sheath or shelly cylinder ; 

 and the pallets, which had been previously kept pressed 

 against the sides, then spring forward and close the open- 

 ing, so as to form an efficacious barrier against all foes, 

 whether Crustacea or annelids. This complicated animal 

 mechanism is entirely enclosed in the sheath or cylinder 

 above mentioned, which is secreted by the mantle and 

 varies considerably in thickness and extent. The inside 

 of the sheath is at its outer or narrower end divided into 

 short strips or ledges, arranged in an imbricated fashion ; 

 the last-formed of these ledges serves as a point d'appui 

 for the blades of the paddles, and it greatly assists the 

 Teredo in closely shutting its doors. The whole of 

 what I have above endeavoured to describe is found only 

 within some hard vegetable substance, either the hull of 



