18 6 ROYAL SOCIETY OF CANADA 



of the organic world is onl_v conceivable on the assumption of continual 

 variation of the germ-plasm, that it actually depends upon this even if 

 these variations come about with exceeding slowness, and are thus in a 

 certain sense difficult." 



In the main thfe former conception of the germ-plasm still holds. 

 It is not altered or affected during the life of the individual bv altera- 

 tions in structure of the body, by mutilations, or by results of use or 

 disuse. Only by nutritive fluctuations may it be affected, and then in 

 the vast majority of forms to such a degree as to produce results obser- 

 vable only vrhen these are cumulative through a large number of genera- 

 tions. Even when thus altered the germ cells preserve some of the an- 

 cestral germ-plasm, and thus remote atavistic qualities may be repro- 

 duced. The greatest variation, however, comes from the mingling of 

 the germ-plasms of the two parents, which occurs in fertilization. This 

 is the perpetual source of the appearance of new characters in a species, 

 the sexual process insin'ing thus a diffusion of such qualities amongst 

 the members of a species; but such diffusion is never completed and 

 variation, therefore, may proceed to an infinite extent. 



I have thus dealt at some length witli the theory of the Continuity 

 of the Germ-Plasm because it is the one which has replaced Darwin's 

 Pangenesis, and because also an understanding of its main points leads 

 to a consideration of a number of facts which suggest quite another 

 explanation of the facts of heredity. 



It is now generally accepted that the germ-plasm is the chromatin 

 in the reduced nucleus of the ovum and in the spermatic cell. Indeed 

 Weismann's ids are but the chromosomes left after the reduction of the 

 chromatin through the formation of the polar bodies. 



It is, therefore, of interest to us to inquire into the history of this 

 chromatin and, for that matter of all chromatin to see if it is such a 

 persistent substance as Weismann claims it to be, and, if persistent, to 

 ascertain why it has this property. 



The current view as to the function of the nucleus is that it is the 

 directive organ in the nutrition of the cell. If it does not elaborate 

 everything in the cell it is an active agent in all the metabolic processes 

 of the cell. It is never conceived of as a passive structure. Gruber's 

 experiments on artificial division of the bodies of Infusoria showed that, 

 while fragments of the cell which contained a portion of the nucleus of 

 the original structure grew and replaced the parts lost by division, those 

 fragments which contained no remnant of the nucleus invariably per- 

 ished. Further, it is imdeniably true that, in the fertilization of the 

 ovum, the substance transferred to the latter is chieflv if not wholly the 

 chromatin of the spermatic element, and this unites with the " reduced '* 



