184 



ANARTHROPODA 



FIG. 214. Photograph of the Protozoans in one twentieth of a drop of stagnant 

 water. 



and inasmuch as two new animals are formed by the halving 

 of the parent the tiny creatures may never die of old age, 

 but so long as food and environment are favorable live 

 millions of years. They are therefore sometimes spoken 

 of as the immortal animals. The Protozoa are most numer- 

 ous in stagnant water where as many as ten thousand may 

 be present in a single drop. Ordinary drinking water, 

 however, seldom contains more than a dozen in a quart, 

 and good spring water often has none, 



