CHAPTER XI. 



PHENOMENA ACCOMPANYING FERTILIZATION. 



In the preceding chapters we have endeavored to show that 

 continued metabohsm leads to changes in the organization of 

 Protozoa whereby phenomena of a cycHcal nature in the Hfe history 

 are possible. Among such changes are those which underlie 

 activities at periods of sexual maturity including gamete formation. 

 In the present chapter I wish to consider the activities which take 

 place immediately before, during, and immediately after fertilization, 

 phenomena which are involved in an^- attempt to interpret the effects 

 of fertilization. Here we have to do with protoplasm which has 

 become so changed in organization that further metabolism is 

 impossible as in highly specialized gametes, or with protoplasm 

 which is so little changed that metabolic activities are still possible. 

 The special problems to be considered in this connection are: 



(1) The environmental conditions under which fertilization occurs; 



(2) fertilization tA^pes; (3) the internal phenomena of maturation 

 and reduction in mmiber of chromosomes; (4) the immediate meta- 

 gamic internal activities involved in reorganization; (5) partheno- 

 genesis. 



I. THE ENVIRONMENTAL CONDITIONS OF FERTILIZATION. 



(a) Ancestry.— Attempts to analyze the conditions under which 

 fertilization by fusion of gametes, or by conjugation, takes place 

 have been made in relatively few cases. Since the first of such 

 attempts, and the majority of later ones, have to do with the 

 conditions of conjugation in ciliates we may consider these first. 

 Of the three conditions cited In' Maupas (1889) as necessary for 

 fruitful conjugation— sexual maturity, diverse ancestry, and hunger 

 —the last one only has to do with environmental conditions. The 

 second condition, however — diverse ancestry— was considered so 

 important by IVIaupas and has been so frequently called upon in 

 explanation of results obtained by many subsequent investigators, 

 that it cannot be ignored. Maupas found that individuals of the 

 same ancestry either would not conjugate at all among themselves, 

 or if they did the ex-conjugants were weaklings and soon died. 

 He also found that, with other evidences of degeneration, closely 

 related indi\'iduals of extreme old age showed a tendency to con- 



