EVOLUTION OP THE COLORS OF BIRDS. 21 



latter can nourish itself and grow without being influ- 

 enced in its nature by its nurture." 



The above discussion of the views of Weismann and 

 his opponents is merely intended as a statement of 

 the case in an unprejudiced light so that a provis- 

 ional conclusion may be reached, at least on some of the 

 points in dispute. A brief summary of the details in 

 which the two factions agree and differ may now be 

 given: They agree: 



(1.) In the immortality of protozoa. 



(2.) That mortal metazoa have been evolved from 



immortal protozoa. 



(3.) That the reproductive cells have been set 

 apart by the principle of the division of labor. 

 Weismann claims: 



(1.) That there are two forms of plasma, germ- 

 plasma which has a formative and cytoplasma 

 which has a nutritive function. 

 (2.) That the germ-plasma has the immortality of 



protozoa, while the cytoplasma is mortal. 

 (3.) That the two plasmas are mutually isolated. 



Hence: 



(4.) That whatever may affect the cytoplasma of 

 the body-cells can have no influence on the 

 germ-plasma of the ovary. Or, in other words, 

 that acquired characters cannot be inherited. 

 His opponents claim: 



(1.) That there is only one form of plasma which 

 may be called either somatoplasm or idioplasm. 



(2. ) That, inasmuch as every individual is formed 

 by repeated cell divisions of the germ-cell, 

 there is an immortality of somatoplasm. 



(3.) That the inheritance of acquired characters 

 is not in opposition to any known biological 

 law. 



