DIFFERENTIATION IN CILIATES 77 



The ciliates have solved the j)rohlein of perpetuating 

 complex adult structure by cyclical dedifferentiation. The 

 life cycle of a ciliate is such that, after a certain period of 

 growth, something is changed in the unstable equilibrium 

 of some systems. The old structures disappear and the 

 properties of the predividing organism are such that phylo- 

 genetically primitive conditions and corresponding struc- 

 tures are formed. 



Data on the chemistry of cell division are scarce. L. Rap- 

 kine has shown that in the sea-urchin egg, before division, 

 there is a considerable increase of the — SH groups. This 

 has been extended to apostomatous ciliates [E. Chatton. 

 A. Lwoff, and L. Rapkine (1931)]. But, except for this, 

 we have no data on the nature of the changes, and it ap- 

 pears of utmost importance to obtain information concern- 

 ing enzymatic activities preceding division in ciliates. 



