1 8 MINUTE MARVELS OF NATURE 



The beauty of the markings of the frustules 

 cannot be readily seen in the living- diatoms ; but 

 the skeleton shields, when cleansed of their living 

 matter by heating to red heat or dissolving by 



Fig. lo. The centra) portion of the group of silicioiis 

 diatom-shields shown at Fig. 4, more highly magni- 

 fied. 



nitric acid and magnified, reveal to perfection their 

 wonders of symmetrical precision and minuteness. 

 One of the cleaned shields from a marine form 

 is exhibited in F"ig. 9. Two hundred of these, 

 placed edge to edge, would scarcely extend one 

 inch ; yet this is a very large form, comparatively 

 speaking. The lines and markings on some 

 species are estimated at about i -76,000th of an inch 



