50 MORPHOGENESIS IN CILIATES 



In apostomatous ciliates, the number of kineties remains 

 constant throughout the cycle. But owmg to the great dif- 

 ferences of size, the distance between kineties varies enor- 

 mously from the tomite to the mature trophont. In other 

 parasitic ciliates, the phenomena are quite different. Ich- 

 thyophthirius multifiliis has been studied by H. Mugard 

 (1947). The mature trophont has approximately 2040 

 kineties. This trophont encysts, undergoes palintomy, and 

 gives rise to a great number — approximately 2800 — of 

 "theronts" or hunting forms. The theront has only 43 

 kineties. At the equator of the ciliate, the distance between 

 two kineties is approximately 1 ft in the mature trophont 

 and 1.5 jji in the theront. Despite considerable changes of 

 the value of the surface, the distance between two kineties 

 remains approximately constant. 



What is the mechanism of the variation of the number of 

 kineties? We may start from the theront, the kineties of 

 which are practically bipolar. During the growth, some 

 kineties are interrupted; a multiplication of kinetosomes 

 takes place. Ramifications are produced, and the new 

 branches find their place between two other kineties. Thus, 

 new kineties are formed during the increase of the surface 

 of the cortex. During palintomy, short sectors of kineties 

 are to be seen on the surface of the tomont. The division 

 of the ciliate is accompanied not by a division of bipolar 

 kineties, but by an apportionment of segments of kineties. 

 The result is, at each generation, a reduction of the number 

 of kineties. It is only after the last division that the tomite 

 regularizes its ciliary system, which becomes bipolar. Thus, 

 in Ichthyophthirius, there is no genetical continuity of kine- 

 ties, but reorganization of kinetosomal material in longi- 

 tudinal kineties. And the nature of cortex equilibrium is 

 such that throughout the cycle, despite considerable varia- 

 tions of size and owing to a constant change of the number 

 of kineties, the distance between two kineties remains con- 



