34 



GENERAL CONSIDERATIONS 



The longevity of a ciliate's protoplasm in the past is shown by the 

 fact that it is before us today and it has a possibility of indefinite 

 longevity in the future. We know very little about the secrets of proto- 

 plasmic organization which underlie continued life, but we can analyse 

 some, at least, of the conditions under which it maintains its animation. 

 A proper environment and adequate food are essential factors. These 

 lead to growth and to reproduction by division. We have seen that these 

 latter bring about a reorganization and a return to full metabolic ac- 



Figure 13. U role plus 

 mobilis Engelm. Conjuga- 

 tion and merotomy. (After 

 Calkins, 1921.) 



tivity. The periodic restoration of these processes might well be enough 

 to ensure protoplasmic longevity, as seems to be the case with the 

 animal flagellates. At endomixis the ciliate macronucleus follows the 

 fate of other parts of the derived organization; a new one is formed 

 from the fundamental organization, and the result is, again, increased 

 vitality of the protoplasm. This phenomenon, recurring every thirty 

 days, ensured the longevity of Parameciuni aurelia in Woodrufl^'s hands 

 for many years and through thousands of generations by division. As 

 Woodruff states, it may be adequate, indeed, to ensure indefinite life 

 in the future, as division alone is apparently adequate for animal 

 flagellates. 



In a conjugation test made with Uroleptus, the results showed that 

 if the series is sixty or more days old, the individuals multiply by 



