REGENERATION IN URONYCHIA 115 



If cell division were merely a matter of mass relation of cell 

 body to nucleus then by cutting the cell with only a small portion 

 of the nucleus this relation would be changed to the advantage 

 of the nucleus. We should expect, on Hertwig's theory that the 

 regulatory process of the cell which brings about cell division 

 would be operative under these changed conditions, but such is 

 not the case. Division instead of being hastened, is retarded and 

 in some cases, prevented altogether. 



Wallengren's careful and accurate description of the regen- 

 erative processes in hypotrichous ciliates, including Uronychia, 

 shows that all of the appendages are discarded and new ones 

 formed in the cell before division occurs. This regeneration 

 which for Uronychia, I have amply confirmed, occurs before the 

 nucleus is entirely concentrated, (cf. fig. 2) and before the nucleus 

 divides. This indicates a condition in the cytoplasm at this 

 time not present at other times, a condition which may be due to 

 the presence of substances at certain periods of cell life. This 

 condition at times of division is analogous to the -condition at 

 times of regeneration, that is, regeneration is equivalent to this 

 precocious cirri and membranelle formation at division. We 

 have seen that the power to regenerate is much reduced at periods 

 immediately after division and then only when the full comple- 

 ment of micro- and macro nucleus is present ; we have seen further- 

 more, that this power increases towards the next division period 

 and is at its maximum at the time of division. 



These facts are best interpreted on the supposition that sub- 

 stances are formed in the nucleus and transferred to the cyto- 

 plasm where they or the products of their activity, accumulate 

 until a condition analogous to saturation is reached. Cutting 

 the cell at this period results in the exhaustion through regen- 

 eration, of these substances so that cell division is retarded in 

 forms where the division process is not already started. The 

 facts, therefore, lend support to deVries' and Hertwig's view that 

 the nucleus gives off to the cytoplasm during the vegetative 

 stages, certain formative substances peihaps of the nature of 

 enzymes, which are exhausted with the regenerative processes 

 accompanying division. 



