54 



MORPHOGENESIS IN CILIATES 



In the region where 11 exists as a row, a kinetodesma is 

 visible. There is no kinetodesma further up. The kineto- 

 desma has disappeared, and it seems highly probable that 

 its disappearance is responsible for the scattering of kineto- 

 somes. The kinetodesma appears as the framework of 

 kinetosomal order, the visible agent by which the hitherto 

 unknown "morphogenetic forces" exert their mysterious 

 orienting action. 



Fig. 20. Phoretophrya nebaliae. Formation of the hypertomite, show- 

 ing the elongation of kineties 1, 2, 3. 



During morphogenesis of the trophont of Phoretophrya 

 nebaliae, some kineties increase in length. Is this purely 

 a passive phenomenon, corresponding to the stretching, 

 under cytoplasmic pressure, of a fiber, anchored at its an- 

 terior and posterior ends? Or is the stretching active, that 

 is to say, the result of elongation of certain fibers by syn- 

 thesis of new material? The latter hypothesis seems plaus- 

 ible. If it is admitted, it is also necessary to admit that the 

 unequal growth of the different kinetodesmas is the expres- 

 sion of an unequal distribution of the substances inducing 

 the growth of kinetodesmal fibers. Nevertheless, the un- 

 equal development of kinetodesmas, even if it is held re- 

 sponsible for the torsion, cannot be the cause of asymmetry; 

 it would rather be an effect of this asymmetry. 



Let us consider now a more remarkable example of tor- 

 sion. 



