(1KNERATION, SEX AND ONTOGENY 213 



The same is true of the animalcules of stagnant water. If 

 some water in which there are apparently no living organisms, 

 however minute, be allowed to stand for a few days, it will come 

 to be swarming with microscopic plants and animals. Any 

 organic liquid, as a broth or a vegetable infusion exposed for 

 a short time, becomes foul through the presence of innumerable 

 bacteria, infusoria, and other one-celled animals and plants, 

 or rather through the changes produced by their life processes. 

 But it has been certainly proved that these organisms are not 

 spontaneously produced by the water or organic liquid. A few 

 of them enter the water from the air, in which there are always 

 greater or less numbers of spores of microscopic organisms. 

 These spores (embryo organisms in the resting stage) germinate 

 quickly when they fall into water or some organic liquid, and 

 the rapid succession of generations soon gives rise to the hosts 

 of bacteria and Protozoa which infest all standing water. If 

 all the active organisms and inactive spores in a glass of water 

 are killed by boiling the water, "sterilizing" it, as it is called, 

 and this sterilized water or organic liquid be put into a sterilized 

 glass, and this glass be so well closed that germs or spores can- 

 not pass from the air without into the sterilized liquid, no living 

 animals will ever appear in it. It is now known that flesh will 

 not decay or liquids ferment except through the presence of 

 living animals or plants. To sum up, we may say that we know 

 of no instance of the spontaneous generation of organisms, and 

 that all the animals whose life history we know are produced 

 from other animals of the same kind. "Omne vivum ex vivo," 

 "All life from life." 



The method of simple fission or splitting binary fission it 

 is often called, because the division is always in two by which 

 the body of the parent becomes divided into two equal parts 

 into halves is the simplest method of multiplication. This 

 is the usual method of Amwba (Fig. 120) and of many other of 

 the simplest animals. In this kind of reproduction it is hardly 

 exact to speak of parent and children. The children, the new 

 Amoebce, are simply the parent cut into halves. The parent 

 persists; it does not produce offspring and die. Its whole body 

 continues to live. The new Amoebae take in and assimilate food 

 and add new matter to the original matter of the parent body; 

 then each of them divides in two. The grandparent's body is 

 now divided into four parts, one fourth of it forming one half 

 15 



