PROBLEMS OF EQUILIBRIU:\I 63 



Therefore, the fact that kiiu>ties are cut in two eciual parts 

 would mean that the niicklle of the kinety corresponds to 

 the middle of the underlying "morphogenetic field." 



The division of a ciliate into two equal parts is the most 



Fig. 26. Plagiospira crmita. (a) Dorsal view, showing the short thig- 



motactic kineties. (1)) Division. The thigmotactic kinetics are cut in 



their middle by the oblique striction zone. A and B, preoral kineties. 



common and certainly the primitive condition. But some 

 ciliates produce a bud, that is to say, a small opisthe. This 

 happens in many parasitic ciliates or in suctorians w^hich 

 feed for long periods on other ciliates and are, if considered 

 from a nutritional point of view, '^biochemical parasites" 

 [see A. Lwoff (1944)]. 



