28o 



J. CULVER HARTZELL 



Fig. 10. — Mold of the exterior. 



is a mold oj the interior. (See Figs, gc, ii, 12.) (c) It follows from 



the above that, if the hollow organism become filled with and im- 

 bedded in material of the same, or different, composition, and then 



disappears, we have left a 

 mold of the exterior in the 

 matrix and a mold of the 

 interior in the form of a 

 kernel. (See Figs. 9c, 10.) 



III. The term cast is used 

 to designate the material 

 which takes the place of the 

 original, whether by replace- 

 ment due to a molecular 

 process or to infiltration. It 

 is also used to designate the 



material occupying the mold made by the exterior or interior. (See 



Figs. 10, 12, 13, 14.) 



If the mold described under II {a) becomes filled, we have a cast 



of the exterior. If the mold described under {h) becomes imbedded, 



its imprint will be a cast of the 



interior. If the space between 



the two molds described under 



(c) becomes filled, we have a cast 



of the exterior and interior, and 



therefore an object the same in 



shape and outline as the original. 



If the original be gradually 



replaced molecularly by some 



mineral, we have a cast which 



will show its shape, outline, and 



internal structure. 



From the foregoing it is obvious that an original is the organism 



itself; a mold, the reverse of the original; and a cast, the counter- 

 part of the original. The latter may or may not show the internal 



organic structure. 



It follows, therefore, that the only way one may know whether 



the markings on certain molds or casts represent the exterior or 



Fig. II. — Mold of the interior. 



