36 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



processes of life, digestion, assimilation, respiration, excretion, 

 secretion, and to reproduce others of its kind. It is this 

 wonderful capacity for living that separates the one-celled 

 organisms, simple as they may seem to be in comparison with 

 higher plants and animals, by a wide gulf from the most com- 

 plex of inorganic bodies. Some scientists have been able to 

 produce in their laboratories particles of matter that closely 

 resemble, in many respects, these simple organisms, but none 

 has yet been able to endow these creations with the subtle 

 power which we call life. 



We have found, moreover, in our study of the Protozoa that 

 while they are each composed of but a single cell, or, rarely, of 

 a group of cells temporarily united to form a colony, the cell 

 itself may be very complex in its structure, some parts of it 

 adapted for protection, other parts for locomotion or food 

 getting. There may be a definite upper and lower side and 

 anterior and posterior end, and there may be many other 

 specializations of parts that especially fits each of these one- 

 celled animals to live in its particular place. 



Spontaneous Generation. People used to believe that many 

 animals were spontaneously generated. When myriads of fly 

 larvae mysteriously appeared in a mass of decaying matter it 

 was supposed that they had been generated there spontane- 

 ously. When great numbers of frogs or insects or any other 

 animals appeared from some unknown source the phenomenon 

 was explained by spontaneous generation. Long after it had 

 definitely been shown that none of the larger animals could 

 arise in this way, many still held to the belief that at least the 

 simplest animals and plants arose in this way. If a vessel of 

 ordinary water in which there are apparently no living organ- 

 isms be allowed to stand for a few days it will usually be found 

 to be swarming with minute animals and plants. The source 

 of this life was a mystery to the older observers, but we know 

 now that some of these organisms come from others that were 

 already in the water and some come from spores that are 

 constantly in the air. If a bottle of water is boiled thoroughly 

 enough to kill all the organisms in it, and then closed so tightly 

 that no germs or spores can reach it from the outside, it will 



