REVERSIBILITY OF MORPHOGENESIS 17 



reported that apiece of a ciliate, in this case Uronychia, containing 

 a piece of the macronucleus but no micronucleus is capable of 

 regenerating into a normal individual. This point is of interest 

 and ought to be investigated further. 



The fact to be noted in this connection is that whenever de- 

 differentiation occurs it is limited in its extent and does not lead 

 to any visible disintegration or dedifferentiation of nuclear sub- 

 stance. There is always a differentiated residuum which might be 

 considered to have a relatively stable germinal differentiation 

 and doubtless has, for re differentiation of a dedifferentiated piece 

 leads to formation of a definite hereditary pattern. From this 

 it is evident that dedifferentiation is limited to relatively super- 

 ficial and transient cell structures. 



In connection with the fact that dedifferentiation is limited in 

 its extent to superfiical (somatic) structures and does not affect 

 germinal or nuclear structures, and the theory proposed above that 

 the dedifferentiation process is closely related to phenomena of 

 autolysis, it seems to me significant to note that nuclei of tissues 

 are much more resistant to autolysis than the cytoplasm. A 

 residuum remains after prolonged autolysis of tissues, which 

 consists largely of nuclei and nuclear debris. This is chemical 

 evidence indicating that nuclear structures are chemically speak- 

 ing relatively stable, and hence on the above interpretation we 

 should expect that dedifferentiation would visibly involve only 

 cytoplasmic structures, which it does. I can verify this point 

 from observations on various protozoa; for example Colpidium 

 and Paramecium which were ingested by Bursaria. The macro- 

 nucleus persists in a recognizable condition much longer than 

 the cytoplasmic structures of the food material in the digestive 

 vacuole. 



IX. SUMMARY 



I. Dedifferentiation of the gullet in the ciliate Bursaria always 

 occurs before division, encystment, and regeneration of lost 

 parts of the cell. It also occurs spontaneously and is not always 

 followed by division, encystment or regeneration. 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 24, NO. 1 



