28O A. RICHARDS. 



however, there arises endogenously the new prophase chromo- 

 some. The old chromosome is an earlier existing "endogen" 

 for the foundation of the new. She regards the chromatic sub- 

 stance as the persistent continuing portion, while the achromatic 

 substances between cell generations are lost. My observations 

 on Fundulus bear out the main facts of this conclusion, although 

 the details of the process differ. 



It remains finally to inquire whether any significance attaches 

 to the fact that the conditions described in this paper occur in 

 tissues that are dividing rapidly. In all cases where persistent 

 chromosomal structures are found the period of interkinesis is 

 comparatively short; the question may be raised therefore 

 whether in cells in which the interkinesis is of long duration the 

 fusion of the vesicles is not more complete and the continuity 

 perhaps lost. It seems to the writer that this is probably not 

 the case, although the latter cells may require a more delicate 

 technique and more close observation to discover that the vesi- 

 cles are persistent entities. The fact that there is no resting 

 period intervening between the maturation divisions and that 

 the chromosomes in this case persist from one mitosis to the 

 next in itself argues for the view of continuity elsewhere. We 

 may look upon this discrete nature of these chromosomes as a 

 manifestation of a condition that is general for cells and is 

 merely emphasized in this particular case. A somewhat similar 

 principle is that of a catalyzer, which is not able to initiate 

 a reaction, but merely to hasten one that ordinarily takes place 

 at a much slower rate. A second reply to the question of the 

 significance of the above mentioned fact is that usually cells 

 which divide very slowly are not of hereditary importance since 

 those cells which bear the hereditary qualities usually divide 



with fair rapidity. 



SUMMARY. 



The chromosomes in the eggs of Fundulus can be traced from 

 the metaphase of one cell generation through all the stages of 

 mitosis and interkinesis as continuous structures which give 

 rise to the prophase chromosomes of the next mitosis. As they 

 pass toward the poles in the anaphase they gradually loosen up, 

 showing their constituent chromomeres, and finally form vesicles 



