im 



THE AMERICAN MUSEUM JOURNAL 



HEREDITY-CHROMATIN- 



A CENTER OF 



PHYSICOCHEMICAL ACTION " 



Osborn's book. Tlir (Jiiiiin and Ero- 

 hitiim of Life, discusses four gi'eat 

 interrelated evolutions guided and 

 controlled by four great sets of inter- 

 acting energies. One is the evolution 

 of tlie earth itself, whicli becomes the 

 environment or liome of any organ- 

 ism, to wliich it must adapt itself or 

 die ; another is the great world of 

 plants and animals among which any 

 organism lives, its life environment, 

 where also it must adapt itself or die 

 and end its race — in other words 

 where "selection" acts to preserve or 

 eliminate it. The other two are re- 

 spectively the visible and the invisible 

 (the latter purely speculative) evolu- 

 tions that take place in the organism 

 itself, that is (1) the evolution of the 

 body which is temporary and will die 

 and (2) the evolution of the heredity- 

 chromatin of the germ, that connec- 

 tion between organism and organism 

 of successive generations, which does 

 not die and represents the continuity 

 of life from the beginning until to-day. 



The heredity-chromatin (shown 

 black in the figures), always in a sur- 

 rounding protoplasm (shown grayish 

 dotted), is visible under a microscope, 

 and certain items of its behavior can 

 l)e observed. Chemically it contains 

 an unusually large amount of jahos- 

 phorus, and is one of the most com- 

 plex of all substances. Scientists be- 

 lieve that it carries the heredity deter- 

 miners, both of the individual and of 

 the species. Under its influence the 

 cell protoplasm divides and subdivides 

 into self reproducing cells. 



T1ic iipjKr fi<lllfc uliotvs (III ifif/ riJl 

 from fill' orurji of u m-a urchin. In 

 litis ri-Hiiti<i siiKje the cliroiiiatiii is 

 cotici'iifrafed into a small xpherc 



III till- iiiidiili' fif/iirc arc cells from 

 riijiiilhi (/roiriiH/ root lip of on 



Ihc 

 onion. 



Hiloir (ire crlls from the einhri/o 

 of a ijiont redirood tree. 



In the large cell in the center the 

 chromatin is seen dividing into rod or 

 sausage-shaped masses. These are 

 grouped in two rows facing each other 

 at the middle of a spindle (the two 

 rows are somewhat indistinctly shown ; 

 note later stage in a central cell of figure next above). Later the cell divides through the 

 middle of the spindle so that one row of the chromatin rods is drawn into one half of the 

 cell and the other row into the other half. The heredity determiners derived from both 

 parents are at first united and then in this way redistributed so that every cell (with certain 

 exceptions) in the developing body of the new organism has an equal amount of chromatin 

 carrying heredity determiners 



