12 MOLLUSC A. 



By careful manipulation, the edges of the leaves 

 which form the mantle can be followed around on their 

 convex edges to where they are joined to each other 

 near the hinge ; then back again to where they are 

 again joined by a narrow neck at the outer end of the 

 concave side ; and then along the concave side to 

 where they again join near the hinge on this side. 



The borders are free and easily Hfted, but care must 

 be taken not to cut or lacerate any portion. The bor- 

 der of the mantle is usually narrow in captured speci- 

 mens ; but it cai^e readily seen that there is a thicker 

 outer portion reaching some distance inside of the 

 fringes. Sometimes the inner side of this border is 

 dark-colored, but often it is not very distinctly marked, 

 though it is an important region for shell-building pur- 

 poses. 



The marks of the border are generally quite easily 

 seen on the inner surface of the valve, and may be 

 detected, either by a difference in color and a slight 

 linear depression, especially in burnt shells, and also 

 by the contour, which is convex, the remainder of the 

 interior of the valve being concave. This portion of 

 the animal deposits the whole exterior of the shell to a 

 considerable depth, as has been described (see, also, 



enables one to both see and handle all of them more easily. 

 The inexperienced not only take them out of the water, but 

 indulge in many useless and objectless researches, which dis- 

 arrange and destroy the 'parts. Care, foresight, and the neces- 

 sity of doing everything with a definite end in view, are needed 

 even in the simplest operations of dissection, and can be prac- 

 tically taught in these and all other operations, if the teacher is 

 disposed to make these lessons useful in their broadest accep- 

 tation. 



