No. 607] DIFFERENTIATION IN THE ORGANISM 



421 



recently sliown that at least the embryonic mesenchymal 

 cells have an unlimited power of regeneration and there- 

 fore can be considered potentially immortal. 



In passing I should like to point out tliat tho uii inter- 

 rupted synthesis of the chromatin during cell prnlifci a- 

 tion may be secondarily influenced by the diti'erences in 

 the cytoplasm thus acquired. The assumption of invari- 

 ability on the part of the chromosome-complexes would 

 imply a further assumption of persistence in the cyto- 

 plasm at least of some unchanged metabolic processes 

 identical for all cells, to which the synthesis of identical 

 chromatin could be referred. 



Differentiation by segregation is a fact proved experi- 

 mentally and many striking examples of segregation of 

 various cytoplasmic materials during cleavage are found 

 in Wilson's and Conklin's work. As result of segrega- 

 tion a number of cell groups appear. The grou]>s are dif- 

 ferent, but the cells of each of tluMii arc similar. The 

 various cytoplasmic substances distributed [o \ho cell 

 groups are specific, can not he built u]i h>- <-clls. wliicli do 

 not contain them and influence the further dcvclopuient 

 of the cells in a definite raannei-. 



These groups of cells ]>rolifcrate and di t'fcicntiate, 

 giving rise to a numbei- of speciflc oi-uaii<. ti-suc- and 

 cells. I)oe< a further si-i-euat i„„ c.f definite Mih-^tances 

 continue at the lime of the flnal >i)ccialization of ti-sucs, 

 are the cell potentialities uTadually narrowc.l by turther 

 differential distribution of cytoi>la>niic con-titucnt>, and 

 finally rendered univalent and ii rcvcr>lhlc [.caving 

 aside the question as to how specific tis-ues aiisc from 

 specific anlages, Loeb in his ]:\<\ book, an im]iortant and 

 stimulating pul)lication, a<lopts the view shared al-^o by 



of the various oi-gair^ of the bedy. a^ bein- due to the de- 

 velopment (d' sprc'/ic rrlls in definite hications in the 

 organism, irhuh u\U <iroir o](t into rh'fiuitc ort/aiis, no 



