70 



MORPHOGENESIS IN CILIATES 



migrate towards the posterior pole. The adult structure is 

 thus formed. 



In Boveria, the preoral system is entirely rolled up "on" 



f g 



Fig. 29. Evolution of Hemispeiridae. (a) Ancistrnm teUinae. (b) 

 Prohoveria loiipedis. (c) Boveria (schematic), (d) Posteroventral 

 view of Boveria^ showing the oral system, (e), (f) Division of Proho- 

 veria. Note the resemblance of the daughter ciliates to the adult Ancis- 

 trum. (g) Predivision of Boveria, showing the anterior position of the 

 oral ciliature. A to F, various preoral and oral kinetics. 



the posterior ''pole" which has been modelled into a circular 

 surface. Before division takes place, the totality of the pre- 

 oral system migrates towards the anterior end and forms an 



