1897.] NEW YORK ACADEMY OF SCIENCES. -313 



preparatory to cutting which is done during the contraction of 

 the posterior adductor and the posterior portion of the anterior 

 adductor. Tlie motion so produced is, in general, upward and 

 backward, though as a matter of fact the axis of motion whicli 

 passes through the umbo, swings with the latter as a center, from 

 the ventral adductor to the posterior and back again with one 

 round of attack. 



The separate action of the adductor muscles may be easily de- 

 termined in fresh specimens by cutting through the different 

 muscles and watching the results. 



The mechanism of boring in Teredo warrants the conclusion 

 that the process has many points of similarity to that just de- 

 scribed. The absence of the ventral adductor is compensated 

 for by the size and position of the so-called posterior adductor, 

 the contraction of which sets in action the rasps of the anterior 

 portion of the shell. The view of Deshayes that the musculature 

 is not fitted to set a boring apparatus in action must be dis- 

 sented from. Nor is it necessary to be satisfied, with Quatre- 

 fages, that a weak musculature is suflflcient for cutting water- 

 soaked wood. The fact is that the posterior adductor is much 

 larger and stronger relatively than the same muscle in the oyster 

 and pecten. The ratio in Pecten of the inner surface of the 

 shell to the area of muscle attachment is, on a liberal calcula- 

 tion, as 9 to ], while in the oyster the ratio is very nearly the 

 same. In Teredo it is as 5 to 1 (in young specimens as much 

 as 3 to 1), and Teredo has the anterior adductor to boot. 

 This fact, together with that of the sharpness and number of 

 teeth, is evidence that the apparatus is very efficient. 



As has been pointed out, the axis of motion passes dorsi-ven- 

 trally through the umbo, and swinging upon their mutual axis, 

 the valves separate in front in answer to the contraction of the 

 posterior adductor. During this motion the teeth of the front 

 part of the shell come into full play in the direction of their 

 greatest efficiency. Previously, of course, the contraction of 

 the pedal muscles has caused tlie application of the front of the 

 shell against the wood which is being attacked ; this as in the 

 Pholads proper. The wood is rasped into very finel}' divided 

 particles which pass into the mouth and through the digestive 

 tract, into the cloaca and so out. The length of the internal 

 processes is such as to bring the point for attachment of the 

 pedal muscles to either side of the center of the spherical shell. 

 It will be seen that this is a matter of mucii importance, for 

 otherwise the pressure of the shell upon the wood would be un- 

 even and we should then have a good tool poorly handled. 



The animal is able, on account of the spherical shape of the 



