64 MORPHOGENESIS IN CILIATES 



When in such parasites kineties are present and bipolar, 

 they are cut not in their middle, but far behind the equator 

 of the animal. In Chromidina elegans, for example, which 

 is attached to the epithelium of the kidney of Sepia elegans 

 by its anterior pole, the first constriction zone separates a 

 fragment one-tenth of the length of the animal. If we con- 

 sider the form of the ciliate with its enlarged anterior ex- 

 tremity, the volume of this fragment is far less than one- 

 thousandth of the volume of the parent. The detached pos- 

 terior part will undergo four to five divisions. At each divi- 

 sion, the constriction zone lies behind the equator. 



The combination of fixation and of some nutritional fac- 

 tors has resulted in the shifting towards the posterior end of 

 the normally equatorial constriction zone. We could ex- 

 press this in terms of an inhibition "gradient." However, 

 considering the fact that all segments are unequal, one is 

 tempted to ascribe this "heterotomy" to a heterogeneous 

 structure of the cortex with properties varying progressively 

 from the anterior to the posterior pole. The constantly 

 flowing endoplasm of the ciliate cannot be considered re- 

 sponsible for this phenomenon. The fact that trichocysts 

 are formed only in the vicinity of the posterior end shows 

 that the "morphogenetic substance" responsible for tricho- 

 cyst formation is localized, whether formed or adsorbed we 

 do not know, in the region where division will take place. 

 This can be understood only if we admit that the cortexes of 

 the anterior and posterior parts are different. 



The fact that heterotomy (or budding) also takes place 

 in suctorians where no kinetodesmas have been detected 

 seems to show, if kinetodesmas are really absent, that the 

 fibers express, rather than control, the properties of the 

 cortex. 



