EVOLUTION OF THE COLORS OP BIRDS. 13 



solely from that part of the nucleus which is purported 

 to be the chief bearer of the germ-plasm, but from the 

 whole nucleus plus a portion of the cytoplasm of the 

 ovum, it is evident that the somatoplasm must have some 

 constructive powers as well as the germ-plasm; but this 

 is the very thing denied by Prof. Wiseman, and if true, 

 what would be the necessity of introducing the germ- 

 plasm at all. The somatoplasm alone would be able to 

 be the bearer of hereditary characters, and we would 

 then have a continuity of somatoplasm instead of a con- 

 tinuity of germ-plasm. 



Prof. Weismann's reply to the criticism of Prof. Vines'* 

 is of especial interest for it contains an epitome of his 

 theories brought up to date. From it, it is possible to 

 comprehend which of his views he still holds and which 

 he rejects, a task of some difficulty in depending upon 

 the series of his collected essays. In reply to the objec- 

 tion of Prof. Vines that an immortal cell could not have 

 changed into a mortal cell by fission unless there already 

 existed within it a latent principle of mortality, Prof. 

 Weismann appeals to the division of labor, saying: 

 " From the one cell which performed all functions comes 

 a group of several cells which distribute themselves over 

 the work. In my opinion, the first such differentiation 

 produced two sets of cells, the one the mortal cells of 

 the body proper, the other the immortal germ-cells." 

 Surely Prof. Weismann does not consider immortality a 

 function of amoeban cells, or, if he does, cannot hold 

 that mortality is another function possessed by the same 

 cells! His explanation of the distinction between im- 

 mortality and eternity is opportune and may throw some 

 light on the subject. By biological immortality Weis- 



*Prof. Weismann's Theory of Heredity; Nature, February 6, 1890, pp. 

 317-323. 



