38 MAN, — THE ANIMAL 



But the ameba has no stomach with glands nor 

 any special glands to provide a digestive fluid. 

 It must be inferred that the protoplasm of the cell 

 has itself the property of producing digestive 

 fluids. After the engulfed food has been in the 

 body of the ameba for a short time, it can be seen 

 to undergo changes in form. There are some 

 parts that apparently cannot be digested, since 

 these are moved to the surface of the ameba's 

 body and eventually discharged into the water. 



When one is studying a number of amebas, he 

 usually finds some of the individuals deeply con- 

 stricted in the middle, and, if one of these is ob- 

 served a few minutes, he finds that the constric- 

 tion deepens until the animal is divided into two 

 equal parts. (Fig. 14.) The result is that two 

 amebas are now found where there was but one. 

 It is impossible to indicate which of the two is 

 parent and which is offspring. The body of the 

 parent has divided into two children but with no 

 parent existing other than as It persists in the 

 bodies of these two children. As the two small 

 amebas grow, they In turn repeat this simple proc- 

 ess of reproduction, but there Is no outside stimu- 

 lus that can be applied that will force such a cell 

 to undergo this process. Where does it end? 

 When does old age begin in such unicellular forms 

 of life? Do these forms ever die? 



From the time that Weismann announced that 



