1904.] MONTGOMERY — CELLULAR BASIS OF HEREDITY. 9 



of the mother cell. The longitudinal splitting of the chromosomes 

 is an autonomous act, whereby each small chromatin mass compos- 

 ing the chromosome (though not the smallest visible granules or 

 microsomes) divides exactly into halves, and the whole complex 

 series of changes leading to the dicentric division .figure seem to 

 have been evolved simply to effect the equal distribution of the 

 daughter chromosomes to the daughter cells. Whether the cyto- 

 plasm divides equally or unequally, the chromatin is always divi- 

 ded and distributed equally. This fact alone has seemed sufficient 

 to most workers to mark the chromatin as the hereditary substance. 



(2) The fact that the chromosomes, the accumulations of chro- 

 matin during ceil division, are fixed in number for all the cell gen- 

 erations of a species. And the strong probability, amounting 

 almost to a fact, that the chromosomes preserve their individual 

 continuity from generation to generation, notwithstanding their 

 great chemical and structural changes during the rest stage of the 

 cell. 



(3) The fact that the spermatozoon, in most respects the very 

 antithesis of the ovum, on entering the egg in fertilization brings 

 in just the same amount of chromatin as that contained in the egg. 

 Not only is this so, but Van Beneden demonstrated as long ago as 

 1883 {Recherches siir la matw-ation de roeiif) that the spermato- 

 zoon brings into the egg just as many chromosomes as are con- 

 tained in the latter. Since we know that the two parents have an 

 approximately equal influence upon the offspring, and since the 

 chromatin is a substance contributed in equal amount by the two 

 germ cells, it is logical to conclude that this substance is the seat of 

 the hereditary growth energies. 



(4) The fact that, despite considerable differences in other 

 respects in their cell divisions, animals and the higher plants show 

 essentially the same behavior of the chromosomes. 



(5) The experiment, first made by Boveri, 1895 {Ueber die 

 Befruchiungs- u?td Eniwickelungsfdhigkeit kernloser Seeigel-Eier), 

 of fertilizing with a spermatozoon the cytoplasm of an egg cell 

 deprived of its nucleus. Such a fertilized egg fragment develops, 

 but shows purely parental characters, probably because all mater- 

 nal chromatin had been eliminated. And two recent papers by 

 Boveri {Ueber fnehrpolige Mitosen, etc., 1902 ; Ueber den Einfluss 

 der Samenzelle auf die LarvencharaJztere, 1903) have shown, with 



