* 



reveals it as a flat sigmoid, or somewhat S-shaped 

 object whose graceful curving lines taper from the 

 middle region — its greatest breadth — to a point at 

 both ends. It is seven times as long as it is wide, 

 and throughout its length runs a middle longitudi- 

 nal line, or rib (the raphe) relieved only at the 

 central region of the test by a navel-like enlarge- 

 ment. At this magnification it looks not much 

 larger than a wasp's wing, to which it may aptly 

 be compared — so gauzy and transparent is this 

 fragile tenement of the microscopic plant. Measur- 

 ing it, however, with a micrometric eyepiece, we 

 find its actual size over all to be exactly one thou- 

 sandth of an inch. 



Such is the short and easy, though complete, 

 description of the form and size of this diatom as 

 seen with a low-power lens. But how can one 

 describe that caress of carmine, now becoming a 

 radiant rose, now going into the greens, now grad- 

 ing into azure and deep mauve as the frustule, 

 viewed by reflected light, is variously oriented 

 over a background of solid black ! Again, as when 

 we looked at the Dinoflagellata, we are met with 

 a marvel of color that is positively unutterable. 

 However, unlike the display of the Dinoflagellata, 



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