GROWTH AND DIVISION 75 



is that any specific event triggers the next following (see p. 295). 

 From the general description of division wq see hov^ the 

 daughter cells are composed of parts both old and new. Endoplasm 

 and nuclear material are halved, but the macronuclear beads are 

 reconstituted and new micronuclei appear as division products of 

 the old. The original feeding organelles go to the proter. They 

 may undergo a slight dedifferentiation during fission, with the 

 oral pouch temporarily disappearing as such, but there is no 

 comprehensive regression and rediff"erentiation as in Bursaria 

 (Schmahl, 1926) or Condylostoma (Villeneuve-Brachon, 1940). 

 Nevertheless, the original oral structures which are at first too 

 large are gradually reduced to proportionate measure in some 

 manner which is not yet understood (Weisz, 1951b). The proter 

 also retains the original contractile vacuole but it has to form a 

 new tail-pole and holdfast. The original tail goes to the opisthe 

 and is also at first too large, but the posterior daughter has a new 

 set of oral structures formed entirely independently of the old. 

 It also develops a new contractile vacuole, though this may be 

 but an enlargement of contributory channels of the old. The striped 

 ectoplasm is divided largely unchanged between the two daughters, 

 although there may be a growing out of stripes and fibers in the 

 formation of the new tail as there is also a post-fissional stripe 

 multiplication in the opisthe to form a new ramifying zone 

 (Schwartz, 1935). There is, however, a marked decrease in the 

 number of lateral stripes because those in the ramifying zone are 

 shifted to the frontal field. Presumably the old body cilia are 

 passed on unchanged, for there is never a time when ciliation is 

 lacking. One should keep in mind, however, the amazing possibility 

 described by Schmahl for Bursaria truncatella^ in which a ciliary 

 molting seems to occur, resorption of old cilia and formation of 

 new ones occurring simultaneously and therefore easily overlooked. 



3. Nature and location of the fission line 



We still know practically nothing of what happens at the division 

 furrow. It seems highly improbable, as Johnson remarked, that 

 the line represents the edge of a plane passing through the interior 

 of the cell though Weisz (1956) conceived that there might be 

 some sort of separation or pre-division of the endoplasm which 

 later comes to expression on the surface. There is no obvious 



