96 HIM ('i.KAi'K CKLi.s IX TLssri: cri.Trur.s. 



lying side by side, but separated by cleavage of the cytoplasm) ma\' be picked out 

 in the fixed i)ivparations, and it might be urged that such were of amitotic origin. 

 This contention can not be proved, however, and it is more ])robable, in view of the 

 lack of i^ositive evidence of amitotic division of tlie cytoplasm, that these cells are 

 either of mitotic origin or have migrated together. 



The problem was attacked by the method of continuous observation of binu- 

 cleate cells (in which the d()ul)le nucleus has ])een sliown to arise l)v direct fission), 

 the object being to .see if the cytoplasm wouUl divide, and in this way give ri.se to 

 two separate mononucleate cells. Several such cells containing twin nuclei were 

 followed, but in eveiy ca.se the cell finally degenerated without dividing, after an 

 observation of shorter or longer duration. As an example, the following may be 

 recorded: In a connective-tissue l)inucleate cell from an 8-day chick heart of 24 

 hours' growth, the jiortions of the nucleus were at first ])ressed closely together, liut 

 after 30 minutes they separated slightly, as in figure 9, and remained apart for 

 2 hours, when they again became pressed together. The cell was ol^served for 11^ 

 hours, and the jirocess of se]iaration and reaiiiiroximation of the nuclei occurr(>d four 

 times during this period. There was no trace of cytoi)lasmic divi.sion and the only 

 changes noted were those mentioned — some shifting of position of the nuclei and a 

 slight decrease in size of the nuclear parts; the latter is believed to be due to pro- 

 longed expo.sure to light. Contiiuious change in shai)e of the cell was followed by 

 change in shajie of the nucleus. 



This ob.servation shows conclusively that the binucleate cell may remain a very 

 long time without direct division of the cytoplasm, and has been confirmed in the 

 case of other binucleate cells. In living cultures the absence of evidence of direct 

 division of the cytoplasm, coml)ined with similar absence in the case of fixed prepa- 

 rations, leaves us with no ground for the assumption that such direct division ever 

 occurs. Even granting that cytoplasmic division occurs at all, the process appears 

 to be so long delayed that it can not he of much imjjortance as a method of cell 

 proliferation. 



This view is in accord with that of ( 'onklin ( 1903, p. 670j, for follicular epithelial 

 cells of the common cricket, but does not coincide with that of Child (1907, c, d. 

 and e), who concluded from this examination of the cells of Moniezia and other 

 animals that amitosis was a rapid method of division which occurred where the 

 stimidus to divide was very great and the supply of nutrition was inadeciuate. 

 Patterson (190S) and others hold similar views. From the cn'idence which tissue* 

 cultures afford, however, I am inclined to agree with Harman (1913, )). 219) that the 

 assumption that amitosis is a more rapid method of cell prohferation than mitosis 

 is hardly justified. 



The ob.servation ju.st recorded also shows tiiat the interi)retatioii of "double" 

 nuclei (.such as those seen in my figures 4, 59, and (50 as separate nuclear sacs 

 touching one another) is correct, for the sacs have been seen to move apart and after- 

 ward to return to their original contact with one another, and to repeat this process. 

 As has been already mentioned, the ai)i)o.sed surfaces of such jiaired nuclei give ri.se 

 to an appearance resembling an intramiclear i)late: such a |)liite has. liowever, not 

 been found bv me in the cells of tissue cultures. 



