CHROMOSOMES AND ECTOPLASM 



of jelly of the same consistency throughout and of equal 

 width. The ectoplasm whence the jelly escaped shows no 

 persistent localized inequality. The changes taking place 

 in it are not confined to any particular region. The egg 

 fertilized after radiation, on the other hand, extrudes jelly 

 of lesser degree of consistency so that the eggs tend to fall 

 out of their jelly hulls. Always is there present in the 

 ectoplasm thereafter an injured region marked by the 

 change in the structure of the ectoplasm as well as by 

 the greater distance of the vitelline membrane at this site. 

 This change in the physical make-up of the jelly is an index 

 of the ectoplasmic injury induced by radiation. In the 

 second place, in the radiated eggs the first cleavage plane 

 passes through the mark of injury revealed after the extru- 

 sion of the jelly. Third, a localized area of injury in the 

 ectoplasm persists through the egg's development and can 

 be traced into the larval worm. 



This observation on the effect of ultra-violet rays on 

 the Nereis egg is supported by my findings on the egg of 

 Chaetopterus; in a similar, but perhaps not so striking a 

 manner, ultra-violet rays affect the surface cytoplasm of 

 this egg.^ 



Since in some cases radiations, especially radium and 

 Roentgen rays, are most effective after nuclear breakdown, 

 it is often held that irradiation does not affect the cell while 

 its nucleus is intact. From this it is argued that radiation 

 directly affects the chromosomes. Indeed, some workers 

 consider that the action of Roentgen rays, for example, is 

 limited to the chromosomes alone. Against this position 

 arguments may be adduced. 



For many cells it has been learned that the display of 

 normal mitotic activit}' depends upon some condition in 

 the cytoplasm which often may even be visible. It is well 



1 Just, iQjod, 1934c. /^^^^L / 



