15S THE MINUTE. 



which hangs over the manner in which these are performed, 

 a mystery which all the perseverance of hundreds of the 

 best microscopists has not yet been able to dissipate. 



6. The power which their structure possesses of taking 

 up the siliceous matter held in solution in the waters, and 

 forming of it solid flint, a process which excites our 

 wonder and which is quite beyond our comprehension. 



7. The uncertainty which attends our conclusions as to 

 their true character. Are they animals ? Are they plants ? 

 The question .is still before the judges. Ehrenberg and 

 other names of high eminence have set them down as 

 animals, but the preponderance of modern opinion is in 

 favour of their vegetable nature. And there are some 

 who would fain make of them a fourth kingdom, neither 

 animal, nor vegetable, nor mineral, but an independent 

 group possessing affinities with all. 



8. Their minute dimensions. The actual size varies 

 exceedingly, according to the species, between one-fiftieth, 

 and one six-thousandth of an inch, or even wider limits. 

 Perhaps, however, we may set down as an average size 

 for an oblong frustule, a length of one-thousandth of an 

 inch, and a width of one-five-thousandth ; that is, that if 

 you could make a chain of them, set end to end, in contact, 

 it would take a thousand specimens to measure an inch, 

 while, if you made a row of them, side by side, five 

 thousand would be required to fill the same extent. 



Highly attractive to a young observer is the variety of 

 life which meets his eye, as he examines, with a good 

 microscope, a drop of water from some pool rich in 



