THE WORLD OF MICROSCOPIC LIFE 45 



food supply of over 99 percent of the animal life 

 of the ocean. The smaller animals, as well as some 

 of the larger ones, feed on them directly and serve 

 in turn as food for fishes and other larger forms. 

 The support of practically all the life in the open 

 sea from the jellyfish to the whales is afforded, in 

 the last analysis, by those minute forms of plant- 

 life which have the property of utilizing as food 

 the mineral substances found in the water in which 

 they are suspended. 



The Protozoa, like the primitive plants, com- 

 monly multiply by dividing. An individual simply 

 constricts into two parts and each assumes the form 

 of the whole organism. As each two becomes four 

 in the same manner and each four becomes eight, 

 and so on in geometrical progression, and as the 

 divisions frequently follow within the limits of a 

 few hours, it is easy to see that in a short time 

 enormous numbers might arise from a single indi- 

 vidual. Many species, especially those that live in 

 fresh water or decaying organic matter, are able at 

 times to assume a spherical form and secrete a 

 covering or cyst of resistant material within which 

 they are able to tide over unfavorable conditions 

 of life. Within these cysts they may undergo pro- 

 longed drying after which, if placed in water, they 



