6 



their ultimate condition fibrous, and having these fibres containing 

 bodies, or appearing to contain them (at least in those belonging to 

 the shell). 



No sort of resemblance appears between the external view of the 

 substance of the hinge and ordinary muscular structure, either in the 

 recent or dried state. When in the latter, the contractile portion of 

 the ligament becomes white and friable. 



Like muscular force generally, the action of this material is placed 

 under a very disadvantageous condition as far as power is concerned, 

 having to act so near the fulcrum and yet to move portions so remote. 



The power exerted by the ligament of the hinge must be immense 

 in certain cases, for instance, the great shell of Chama gigas has a 

 ligament containing this substance. No doubt this shell is opened 

 by some power, for we hear wonderful tales of ropes being bitten off 

 which have accidentally got between the valves ; now it is evident 

 that in order to bite, the valves of the shell must be opened a given 

 distance by some method, and no one doubts that the ligament is con- 

 trived for this purpose ; and as in the ligament no structure appears 

 capable of contracting but that of which I have spoken, it is fair to 

 presume that this is the source of power. The two valves of this gi- 

 gantic conchiferous animal weigh frequently one hundred weight, con- 

 sequently the power to be exerted in order to separate one valve from 

 the other must be immense, as the ligament is not -^ part the distance 

 of the entire valve behind the hinge. 



It appears extraordinary that an organ like this, so remote from the 

 animal, should possess anything more than physical powers, or should 

 possess any power analogous to muscle which can only be maintained 

 by the blood or vital fluid of the creature, and presence of nerves, 

 therefore, if this be endowed with contractile force, it offers a singular 

 anomaly in the animal kingdom. 



It has appeared to me, that the condition of this organ has been 

 hitherto overlooked, and that its structure in the various species is de- 

 serving further investigation than that which I have bestowed upon 

 it ; still I have considered that there was sufficient interest in the ob- 

 servations that I have already made, to lead me to bring them 

 before the notice of this Society this evening. 



