230 The Science of Life. 



and nutrition, may operate through the body on the 

 germ, acting as stimuli on its variable primary consti- 

 tuents. This does not amount to saying that changes 

 on the body can, as such, affect the germ and become 

 transmissible; and the dominant idea of his Romanes 

 lecture is, furthermore, that we call environmental 

 forces efficient causes of change when we are only 

 warranted in calling them stimuli. 



Thus, as causes of variation, Weismann has sug- 

 gested : 



(1) The influence of the environment on the germ- 

 plasm of the primitive Protists. 



(2) The permutations and combinations of vital sub- 

 stances and qualities involved in the processes of 

 maturation and fertilization. 



(3) The stimuli of nutritive and other environmental 

 conditions upon the germ-plasm within the body. 



The most recent and the most subtle of Weismann's 

 theories bears the title "germinal selection". It is a 

 suggestive hypothesis, but difficult to state in a few 

 lines. All are familiar with the Darwinian concept of 

 the struggle for existence, and the selection or elimina- 

 tion of individuals; Roux and others have elaborated 

 the idea of a struggle of parts within the organism and 

 of a corresponding intra-selection ; there is also often 

 a struggle among potential ova and among possibly 

 effective spermatozoa ; but Weismann, after his manner, 

 has carried the selection idea a step further, and has 

 pictured the struggle among the determining elements 

 of the germ-cell's organization. It is at least conceivable 

 that the stronger "determinants", i.e. the particles 

 embodying the rudiments of certain qualities, will make 

 more of the food-supply than those which are weaker, 

 and that a selective process will ensue. 



Let us suppose a case in which, through congenital 

 variation, a structure is undergoing gradual degenera- 

 tion ; the germinal aspect of this may be that the deter- 

 minants corresponding to the structure in question are 

 weak in the germ-cell ; but as the result of the germinal 

 selection they will tend to be further weakened, until, 

 indeed, they disappear. 



