METHOD OF CELL DIVISION IX MONIK7I A. -V 



It is certainly most strange, if mitosis occurs periodically 

 or in waves as Richards suggests, that neither Richards nor 

 Young nor I except in tin- case above mentioned have hap- 

 pened to ob-er\e any of these waves of mitosis in the numerous 

 animal- t hat we ha\ e -ectioned. All the evidence which we have 

 obtained indicates a remarkable infrequency and a scattered 

 occurrence of mito-i-. 



lint tin- argument ba-ed on mit<>-is is not direct evidence 

 lor or auain-t the occurrence of amit<>-i-. \\'heii \\ e tind the 

 picture- \\hich I have figured occurring frequently and confined 

 to re- ion- in which the nuclei are knoun pn-iii\el\ to be incr 



in number in -ome \\.iv. the direct e\ ideiice for the occur- 

 r< -in e "I amito-i- seems to me to ha\e far greater value than any 

 indin-c t e\ idence l.a-cd on the treojueiuA or infre(|iienc\- of 



mitosi 



Mi pagi i . lianl- that in th<- primordium of 



theo\ar\ and duct- the re-jon .if unclear increase is at thepe- 



ripherv and that it i- here that mito-i- i- chielly found. 



Wit h the latter statement I jree, bul I imd it difticuh to mxler- 



-land the v:i"'ind- I-T hi- ("iichi-ioii that unclear increase i- 

 niilined to the pel i| iliei-\ . ( CttainU' tlie iiM'i'ea-e in the number 

 <il mil lei at llie peiipheiA i- n.it \i it, \\hile in the central 



ion "I the pi inioidinin the nuclei are \ ei \ niimeioii-, cm \\ded 

 i li.-e together. M"ie. .\ ei , these central nuclei are in earl\ -t.: 

 \et\ much -mailer than the peripheral. I nle-- there ha- be, n 

 e\ten-i\e mi^iaiiiiii from ihc periphery to\\ard the center it i> 

 impossible to accoimt for the i^tvai number of nuclei then except 

 b\ pM'lileiation. Ki< hard- ha- failed to lind amitn-i-, in thi- 

 region, but 1 ha\e found nnmeroi: ( if \\hat I regard as 



amito-i- in hi- -liile-. I l< maintain-, that the central nuclei 

 are be^innin^ ditleieiil iat ion (p. [50). I have been unable to 

 Observe an\ \i-ible dilleientiation in this region at the-e -t.: 

 and be-i<le- the-e ct.i\\led nuclei are on the average much 

 -mailer than anv nuclei of the \\hole |)rimonlium after the vi-iMe 

 difli'fentiation ha- be-nn. In later st .\lieu. as I believe. 



|)iolil\'ration become- le-- rapid, the-e nuclei -ladiialh enlarge 

 a-ain and became more \\idely -eparati'd and then visible dif- 

 ferentiation begin-. For the-e reasons I am unable to agree with 



