TEREDO. 



151 



action and extended, diverge considerably ; so that the 

 excretal tube discharges the exhausted water, faeces, 

 and woody pulp backwards, or in such a direction as 

 not to interfere with the current which passes into the 

 branchial and alimentary tube. Clark insists that the 

 anterior adductor muscle in Teredo, as well as in Pholas, 

 is a "genuine cartilage, which is a secretion from 

 glands.^^ This notion is opposed to that of other phy- 

 siologists; and I merely mention it to show how difficult 

 it is for one not conversant with such matters to decide 

 the question, or even to understand how a cartilage or 

 ligament can be secreted in the manner suggested by 

 my late friend. He also stated that the pallets act as a 

 sort of force-pump, to facilitate the flow of water through 

 the long canal. M. Cailliaud supposes, on the other 

 hand, that the use of those appendages is to macerate 

 such food as is too bulky to enter the tube. I cannot 

 accept either view. The one is hypothetical, and does 

 not accord with our knowledge of the nature of 

 the animal. The other assumes that the pallets lie 

 inside the alimentary tube, or at its orifice, neither 

 of which is the case ; they are placed at the outer 

 base of that tube, when it is protruded in search 

 of food. Valenciennes and Quatrefages consider the 

 posterior muscle to be that which attaches the pallet- 

 supporting ring to the sheath. Clark " perceived in the 

 centre of each plate a decided muscular impression. ^^ 

 This I have not seen; but the posterior lobe or " auricle^' 

 of each valve exhibits a scar, precisely similar to that 

 with which the corresponding portion of other bivalve 

 shells is marked ; and the muscle itself, connecting this 

 part in Teredo, is very strong and conspicuous. I 

 should be disposed to regard the muscle, which supports 

 the pallets and is attached to that part of the sheath, as 



