more than five thousand individual frustules, or 

 silicious skeletons of Pluurosigma angulatum, 

 which is the particular species of diatom we are 

 presently to observe. 



There are hundreds of different forms of minute 

 one-celled plants in the sea, but the diatoms are 

 distinguished among them as being the only ones 

 having their soft vegetative parts contained in an 

 outside covering, or case, of silica. It is by the shape 

 and sculpturing of this exterior glass-like skeleton 

 that the species are identified. Twelve thousand or 

 more species have already been named and re- 

 corded; this imposing list, which is constantly be- 

 ing extended, is not due so much to the scientific 

 interest they hold for the "students" of the group, 

 as it is owing to their attraction for those micro- 

 scopists who have made the collecting of them a 

 fatuous, perhaps, but harmless hobby. It may seem 

 incredible, but there have been diatomaniacs who 

 have devoted their lives to the tracking and mount- 

 ing of these generally invisible motes; they have 

 become so adroit in manipulating them under the 

 lens that the arrangement of several hundred dif- 

 ferent forms in orderly and geometric patterns is 

 produced on a single slide with the same precision 



[118] 



