BEHAVIOR AND FUNCTIONS OF THE NUCLEUS 309 



15. Delayed renucleation 



Since Verworn (1892), it has been found in Amoeba and its 

 relatives that the naked nucleus undergoes immediate degeneration 

 in the absence of its normal cytoplasmic environment and is not 

 viable when reimplanted (Comandon and de Fonbrune, 1939b; 

 Lorch and Danielli, 1953). So it is with Stentor and with 

 embryonic cells (Briggs and King, 1955). Cytoplasm in the 

 absence of the nucleus shows a very much slower deterioration. 

 This raises the question: Beyond what period of time is the 

 cytoplasm irreversibly deteriorated so that it can no longer recover 

 after reimplantation of a fresh nucleus? We would like to be able 

 to analyse what goes wrong in enucleated cells and what the 

 nucleus contributes to the maintenance of the cytoplasm. This 

 approach might be especially fruitful if renucleations were made 

 at a time when certain cytoplasmic functions were recoverable 

 and others not. 



Amoebas can recover normal activity and even divide if 

 renucleated 2 days after enucleation (Comandon and de Fonbrune, 

 1939b; Lorch and DanielH, 1953); but the French workers found 

 that practically no recovery occurred when renucleation was 

 delayed to the sixth day. I have a few experiments of this type on 

 Stentor coeruleus (unpublished). Animals renucleated on days 3 and 



4 of the experiment, or 2 and 3 days following enucleation, could 

 recover completely, regenerate the mouthparts, show increase in 

 the number of nuclear nodes following regeneration, and divide. 

 Very likely they would have developed into clones if the difficulties 

 of culturing had been surmounted. A specimen renucleated on 

 day 6 promptly corrected its faded coloration and necrotic turbidity 

 of the endoplasm, but was not able to regenerate. Another, 

 renucleated on day 5 recovered and regenerated incompletely, for 

 although the new membranellar band was normal the mouthparts 

 consisted only of a short tube (Fig. 87). This animal survived 



5 more days on the slide. Apropos of the remarks above, the 

 specimen lost its contractility completely and could be cut into 

 without showing the slightest twich, as if the myonemes had 

 suffered irreversible damage or loss of response. Evidently the 

 fifth day without the nucleus is critical for Stentor cytoplasm and 

 we should have more experiments covering this period. 



