NATURE'S JEWELS. 163 



and eventually to divide. Before this takes place 

 let us, in imagination, take another look at the 

 position of affairs. There are the valves, lifted up 

 and pushed aside, while the zones protect the new 

 formation or cell growth, on which a longitudinal 

 constriction, gradually deepening, embraces the 

 whole contents. On this, the primordial utricle 

 or membrane is being unfolded, completing the 

 division. And now on this membrane the wonder- 

 ful tracings and sculpturings, the exact pattern, or 

 rather, copy, of the parent valves, are developed. 

 The whole presently becomes silicified, and a new 

 valve is formed. The same process is of course 

 going on on the other side ; and when completed, 

 two Diatoms appear where only one existed before, 

 each one having an old valve on one side and a new 

 one on the other. We are watching a Diatom of 

 the linear form. The division is effected, though 

 for the moment the appearance is that of a double 

 Diatom. Presently an opening commences at the 

 forward extremities, as they move slowly along 

 together, which, gradually expanding, at length 

 terminates in final separation, and each Diatom 

 proceeds alone on its destined course. 

 L 2 



