No. 593] 



THE PROTOZOAX LI EE CYCLE 



207 



of cells get stuck together. I have witnessed the fusion 

 of nine Paramecium cmclntiUH cells in .1 single amorphous 

 mass. 



In other forms, notably the parasitic protozoa, proto- 

 plasmic changes at this stage follow two lines of differ 

 entiation. Some cells store up metabolic products in the 

 form of reserves of nutriment and develop into female 

 gametocytes or macrogametes. Others develop into more 

 active male gametocytes and microgametes. In both of 

 these differentiated types if union or fertilization is pre- 

 vented, the cells die a natural death. 



The effects of conjugation or fertilization are almost 

 the same as those following asexual reorganization through 

 encystment. In ciliates cytolysis of the old macronucleus 

 takes place and its substances are absorbed, that is, 

 undergo chemical changes in the cytoplasm. The ma- 

 jority of the maturation nuclei, both in free-living and in 

 parasitic forms, meet the same fate, while a new nuclear 

 apparatus results from the products of the fertilization 

 nucleus or synkaryon. The cytoplasm is renewed in a 

 chemical sense and metabolic activities recommence with 

 renewed vigor; a new race is started. The sole difference 

 from encystment is that reorganization occurs after or 

 during amphimixis and a new hereditary complex is 

 formed in the nucleus, while even this, in endoganious 

 conjugation at least, can not be very different from the 

 condition after asexual reorganization. It is obvious that, 

 if conjugation is the equivalent of fertilization in metazoa, 

 asexual reorganization or endomixis is the equivalent of 

 parthenogenesis. 



What is the significance of these two important phases 

 in the life cycle and how can they lie interpreted in terms 

 of metabolic activities? As we have seen, there is reason 

 to believe that the cell protoplasm becomes progressively 

 differentiated in a chemical sense between division periods, 

 until just prior to division processes take place which do 

 not occur at earlier periods. With division this differ- 

 entiated condition is reduced, possibly through rytoly>is, 

 until a more labile protoplasm results. Now it is not at 



