GENERATIOX, SEX AND ONTOGEXY 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 Avith microscoi)ic plants and animals. Any 

 organic liciuid, 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 tlieir life processes. 

 But it has been certainly proved that these oiganisms are not 

 spontaneous^ produced by the water or organic licjuid. 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 oi-ganic 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 w^ater 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 wdthout into the sterilized hquid, no living 

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

 not -decay or liquids ferment except througli the presence of 

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

 of no instance of tlie spontaneous generation of organisms, and 

 that all the animals w^hose life history we know are jiroduced 

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

 "Ah life from lifc.^^ 



The method of simple fission or sphtting — binary fission it 

 is often called, because the division is always in two — b}' which 

 the body of the parent becomes divided into two equal i)arts 

 — into halves — is the simplest method of nuiltiplication. This 

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

 the simplest animals. In this kind of re})ro(hiction it is hardly 

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

 Amoibce, are simi)ly the parent cut into halves. The ])arent 

 persists; it does not produce offspring an«l di(\ Its whole body 

 continues to live. The new Amabte 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 grand])arent's body is 

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

 15 



