310 WONDERFUL STRUCTURE OF SHELLS. 



This is shown in many waysj for in the structure of 

 Shells there is a general adaptation of the wants of the 

 animal to which they belong. Thus, there are light shells 

 for the floaters and swimmers, strength for the limpets and 

 periwinkles, and other adjustments as needed for others. 

 What can be more wonderful than the apparatus essential 

 to what are commonly called bivalves, or molluscous ani- 

 mals protected by two shells? The hinge which connects 

 them shows a singular contrivance for the necessities of the 

 animal. It is formed entirely of the inner layer of shell, 

 and consists of either a simple cardinal (a hinge) process, or 

 of serrated projections, or teeth as they are called, with cor- 

 responding cavities or sockets into which they are inserted. 

 To this hinge is superadded a ligament, the external sub- 

 stance by which the shells are united, which binds the twO' 

 parts together, and keeps those composing the hinge in 

 their places. This ligament is highly elastic, being com- 

 posed of a number of fibres, parallel to each other and per- 

 pendicular to the valves which they connect. When the 

 animal is undisturbed, the elastic ligament keeps the valves 

 open, and the functions are carried on without any effort. 

 When danger is apprehended, or circumstances require it,. 

 the adductor muscle or muscles contract, overcome the re- 

 sistance of the hinge, and shut the valves close until they 

 may be opened with safety. 



Conchology, is the science which teaches the arrangement 

 of shells into classes, species, etc. Formerly, these beauti- 

 ful productions of Nature were looked upon as merely pleas- 

 ing toys and objects of curiosity, but gradually this inno- 

 cent trifling came to be viewed in its true light, by some- 

 collectors worthy of better employment, who put off childish 

 things and went deeper into the subject. In anticipation 

 of this, shell-collectors began to look upon their treasures as 

 an assemblage of gems, and, indeed, the enormous prices 

 given for fine and scarce shells, joined with the surpassing 



