

jclei become macronudei: Mitotic division Fusion of the nuclei The remaining nucleu 



2 become micronuclei to yield 4 nuclei to yield a diploid divides mitotically 



I 



/licronuclei divide; 

 I begins to divide 



Autogamy 

 is complete 



Fig. 7. Autogamy in Para- 

 mecium aurelia. 



Persistent Rhythms in Gonyautax Polyhedra: 

 How Organisms Tell Time 



Gonyaulax is a marine microorganism. It is single-celled, built like a 

 protozoan, but contains chlorophyll and is capable of photosynthesis. It 

 normally grows at the surface of the sea and can also be cultivated in the 

 laboratory. In addition to being photosynthetic, Gonyaulax can luminesce 

 (i.e., like fireflies and other insects, crustaceae, some molds, bacteria, and 

 algae, it can operate biochemical reactions that release energy in the form 

 of light instead of the more usual heat). It is one of the organisms respon- 

 sible for the brilliant displays of "phosphorescence" seen at night on ocean 

 waves. At least three important functions— photosynthesis, luminescence, 

 and cell division— are carried out in a regular rhythm keyed to the marine 

 habitat of the organism. Gonyaulax photosynthesizes by day, luminesces 

 by night, and reproduces just before dawn. 



18 



