MOLLUSC A. II 



have not been burnt too long, and also as a slight dark 

 stain unevenly distributed, when seen by the naked 

 eye, throughout the layers.* 



In both instances, whether the animal matter alone 

 is present, or the lime and carbon, the form is retained. 

 This fact satisfies the scholars that the hardness of the 

 sliell and its weight is due to a deposit of layers of 

 mineral matter in close connection with a similar series 

 of layers of animal matter. Having examined the shell 

 itself, the next step naturally is to study the parts of the 

 animal which are associated in building it up, and have 

 left their imprints upon it.f 



For this purpose it will be necessary to observe only 

 the upper, exposed side of the soft parts. It will be 

 seen that the oyster itself is inclosed by two leaves 

 delicately fringed on their outer edges, which are 

 dark-colored and double, and of the same outline as 

 the inner white layer of the valve. J 



* Shells which have been bored by sponges or worms will 

 offen have the cells or tubes they have made lined with char- 

 coal, derived from the burning of these bodies. In trying to 

 account for the weight of an unburnt or undissolved shell, by 

 adding the weight of the burnt shell or lime to that of the ani- 

 mal matter, when separated by the action of acids, it should be 

 remembered that the burning or the solution is very imperfect, 

 and leaves unchanged foreign substances, also, which ought to 

 enter into the analysis, if exactness is desired, and that carbon 

 exists in both cases, and is weighed twice. 



t This is literally the case, since a keen eye can detect the 

 form of the gills, palpi, and body imprinted on the internal sur- 

 faces of the valves. 



X In all these'operations and manipulations, where soft parts 

 are to be examined, no great amount of success can be obtained 

 unless the parts are covered by water. This floats them up, and 



