102 BLASTOGENIC VARIATIONS. 



chapter these blastogenic, genetic, or germinal varia- 

 tions will be discussed, whilst somatogenic variations 

 will be treated of later. 



The cause of hereditary variation Weismann ascribes 

 to the direct effect of external influences on the so- 

 called biophors and determinants of the germ-plasm.* 

 These biophors Weismann defines as " bearers of 

 vitality," or the smallest units of protoplasm which 

 exhibit the primary forces of assimilation and metab- 

 olism, growth, and multiplication by fission. All pro- 

 toplasm, both the nucleus and body of cells, is made up 

 of these units. They are the bearers of the qualities or 

 characters of the cells. Determinants, on the other 

 hand, are groups of biophors, and are the particles of 

 germ-plasm corresponding to and determining the cells 

 or groups of cells which are independently variable 

 from the germ onwards. 



The reaction of the germ-plasm to external influ- 

 ences is primarily one of nutrition. The biophors and 

 determinants are supposed to be subject to continual 

 changes of composition during their almost uninter- 

 rupted growth, and these very minute fluctuations are 

 the primary cause of the greater deviations of the de- 

 terminants, which are finally observed in the form of 

 individual variations. The growing determinants must 

 originally differ to some slight extent in the composi- 

 tion of their biophors, as otherwise inequalities of nutri- 

 tion could never effect any transformation, but could 

 only alter their rate of growth. Slight as are these 

 deviations in the determinants effected by inequalities 

 of nutrition, they are nevertheless of great significance, 

 * " The Germ-Plasm," London, 1893, p. 415. 



