CHAPTER VIII. 



PHENOMENA ACCOMPANYING FERTILIZATION. 



In the preceding chapters we have endeavored to show that 

 continued metabolism leads to changes in the organization of 

 Protozoa whereby phenomena of a cyclical nature in the life history 

 are possible. Among such changes are those which underlie activi- 

 ties at periods of sexual maturity including gamete formation. In 

 the present chapter we will consider the activities which take place 

 immediately before, during, and immediately after fertilization, phe- 

 nomena which are involved in any attempt to interpret the effects 

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

 has become so changed in organization that further metabolism is 

 impossible, as in highly specialized gametes, and 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 protoplasmic and the environmental conditions under which 

 fertilization occurs; (2) fertilization types; (3) the internal phe- 

 nomena of maturation and reduction in number of chromosomes; 

 (4) the immediate metagamic internal activities involved in reor- 

 ganization; (5) parthenogenesis. 



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 ciliatcs we may consider these first. 

 Of the three conditions cited by 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 Maupas 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 individuals of extreme old age showed a tendency to con- 

 jugate and that such conjugations always lead to sterile results or 

 to abnormal ex-conjugants which quickly die. 



Largely as a result of these conclusions of Maupas an unwarranted 



