WAX SIMULACRA OF SHELLS. 



229 



seen to be aggregated in star-like clusters, very much like snow- 

 crystals, or the crystals of ice formed on a frosted window-pane. 

 A diagram of this arrangement is shown in text-fig. 1. This is 

 the arrangement assumed by the crystals after slow cooling, 

 when no special methods are used to accelerate the cooling. I 

 have carefully compared by means of sections cut vertically or 

 parallel to the free surfaces, (1) one of my shell-specimens, (2) a 

 block formed by pouring the molten wax into a metal mould, 

 the block being about | in. long by ^ in. wide, and cooled 



Text-figure 1. 



Diagram of stellate arrangement of prismatic crystals of paraffin-wax in 

 the superficial portion of a spontaneously cooled mass. 



spontaneously. I find that in a vertical section from the shell- 

 specimen taken about the middle of the mass, the same stellate 

 arrangement of crystals can be seen. The same arrangement 

 also occurs in a section from the exposed surface. A portion of 

 the lower surface, i. e. that which is suddenly cooled by contact 

 with water, however, shows a different appearance, namely, a 

 number of short irregular lines at angles to one another, marking 

 out polygonal areas which may be the bases of crystals extending 



