HEREDITY 91 



nevertheless avail ourselves of the convenient labels thus 

 offered to us. 



The Galton-Weismann view deserves to be emphasised, 

 because it puts a meaning into the word " inherit " which 

 is rather different to that usually conveyed by that word- 

 or to the sense in which it would apply if Darwin's view 

 were the true one. According to Darwin, parents truly 

 transmit their characteristics to their offspring (by means 

 of the gemmules) . According to the modern view, however, 

 children resemble their parents not, strictly speaking, 

 because the latter have passed something on to them, 

 but because both have been produced from the same 

 germ- plasm. Of course it must be remembered that as 

 a rule the relations of parent and child to the stream of 

 germ-plasm are complicated by the fact that the offspring 

 is the outcome of the fusion of two gametes each from 

 a different stream of germ-plasm. A pictorial repre- 

 sentation of the stream of life under these normal con- 

 ditions, compared with the simple state of affairs where 

 reproduction is carried out without union of the sexes 

 (as for example in the greenfly, or Aphis], is attempted 

 in Fig. 47. 



The relations between germ-plasm and body-plasm lead 

 us on to the consideration of the question of the inherit- 

 ance of ' acquired characters." It is obvious that the 

 characteristics of an organism are dependent upon two 

 factors, (i) its original inborn or innate constitution, which 

 depends upon the germ-plasm (or two germ-plasms) from 

 which it has sprung, and (2) the particular environment 

 to which the organism has been exposed and the ex- 

 periences which it has undergone during its growth and 

 development. These two factors act with varying effect 

 in the case of different characteristics. Thus the colour 



