CHAPTER VII 



REGENERATION 



Stentors have long been the preferred subject for studies on 

 regeneration in the protozoa because of the large size of common 

 species, their amenabiHty to cutting operations, and the elaborate 

 system of cortical differentiations which calls for a substantial 

 performance in morphogenesis and provides a definite end-point 

 for experiments. It must have been a dramatic moment v^hen 

 Nussbaum (1884) extended to the ciliates the earlier experiments 

 of Greeff, 1867, and Brandt, 1877, on heliozoa in demonstrating 

 the general *' divisibility of living matter" at the cell level. Of 

 course cells divide, but now it was shown that man could do the 

 dividing himself with similar results. A year later Gruber (1885a, 

 1885b) published his finding that, in contrast to division, stentors 

 can be cut into three pieces, each of which could produce a new 

 individuality, and his drawing of the regeneration of a trisected 

 stentor was reproduced in dozens of textbooks. He proved that 

 regeneration was in fact complete, for the fragments not only 

 regained the normal form but could then subsequently grow and 

 divide. These studies were carried forward by Balbiani in a series 

 of notable early investigations. Following these pioneers, investiga- 

 tors have turned repeatedly to Stentor as a form in which regenera- 

 tion and reconstitution can be studied within the confines of a cell, 

 the " structural unit of life ". 



I. The course of regeneration 



(a) Oral regeneration and its requirements 



Excision of the head or any appreciable portion of the feeding 

 organelles leads to oral regeneration. A primordium appears on 

 the side of the cell and then moves forward to the anterior end as it 

 develops a new set of ingestive structures. If any part of the 

 original membranellar band and frontal field remain, they persist 

 and are integrated into the new head (Stevens, 1903). But if only 



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