72 MORPHOGENESIS IN CILIATES 



It is generally admitted by protozoologists that one type, 

 if not the type, of primitive ciliate is the Prorodon type. 

 It has an anterior mouth, and diverging from it, a regular 

 set of anteroposterior longitudinal ciliary rows. The sym- 

 metry of the cortex is axial. This hypothetically primitive 

 type has been altered by the asymmetric development and 

 regression of some parts of the ciliary system, by the migra- 

 tions of the mouth, and by the development or alterations 

 of the oral system. A 'Ventral" and a ''dorsal'' face can be 

 recognized in many ciliates — for example, in Gymnodi- 

 iiioides or Foettingeria. But before division, a detorsion 

 takes place. The mouth disappears. The short postoral 

 rows become bipolar. The regular, bipolar, non-differenti- 

 ated anteroposterior ciliary system of the tomont corre- 

 sponds obviously to a primitive type of organization. And 

 here again, the primitive condition is regained before each 

 division. 



Before discussing these facts we have to consider some 

 other types of ciliates, in which it is difficult to recognize 

 primitive and evolved features but which will provide good 

 material for concluding this discussion. 



