274 A - 



Hertwig, G. & P., Gobius and Vesicles in telophases which are 



Arch. f. Mikr. Anat., Crenilabrus thought to be signs of degenera- 



84, 1914. crosses. tion. 



Van der Stricht, O., Triton eggs. Vesicles formed by looping of chro- 



Arch. de Biol., 12, mosomes; figures of resting nuclei 



1892. suggest traces of vesicles. 



(b} Chromosomal Continuity. 



Chromosomal individuality has been so often argued of late 

 years that a renewal of the discussion seems an almost trite and 

 needless repetition. However, in the light of the facts here 

 brought forth it may not be out of place to review the present 

 status of the question. It must be understood that no argument 

 is made that chromosomes are directly transmitted from one cell 

 generation to the next as identities; that conception has long 

 since been abandoned for it has been shown to be inadequate. 

 Rather the argument is that the new chromosomes arise from the 

 same structural substance as the old, a theory of genetic con- 

 tinuity. One prophase chromosome and only one arises from 

 the substance of a single one from the preceding division. It 

 is such a theory which is the subject of this discussion. 



The hypothesis of chromosome individuality dates back to 

 Rabl ('85) who "concluded that the chromosomes do not lose 

 their individuality at the time of division, but persist in the 

 chromatic reticulum of the nucleus" (Wilson). He thought 

 that the disappearance of the chromosome in the reticulum was 

 only apparent, for he could recognize in the reticulum of the 

 salamander nuclei portions corresponding to the chromosomes. 

 The reticulum is formed by the outgrowth of processes, secondary 

 and tertiary, from the chromosomes which while fusing on the 

 neighboring chromosomes, nevertheless, maintain their own 

 identity. 



That Rabl's view regarding the persistence of the chromosomes 

 has not found general confirmation is indicated by the following 

 quotation from Wilson, who, in discussing the theory of chromo- 

 some individuality 1 remarks "that in vast majority of cases 

 the identity of the chromosome is wholly lost in the resting 

 nucleus and the attempts to identify them through the polarity 

 or other morphological features of the nuclear network have, 



i The Cell, p. 300. 



