Organic Natures Riddle 341 



to which any body in ^notion will continue to move on 

 bniformly at the same rate and in the same direction until 

 other force or motion is impressed upon it. 



The fact that new individual organisms arise from both 

 a paternal and a maternal influence, and from a line of 

 ancestors every one of which had a similar bifold origin, 

 [modifies this first law of heredity only so far as to produce 

 & more or less complex compound of hereditary reproductive 

 tendencies in every individual, the effect of which must be 

 analogous to that mechanical law of the composition of 

 forces resulting in the production of a new creature re- 

 sembling its immediate and more remote progenitors in 

 varying degrees, according to (1) the amount of force spring- 

 ing from each ancestral strain, and (2) the compatibihty or 

 incompatibility ^ of the prevailing tendencies, resulting in an 

 intensification, perpetuation, modification, or neutrahsation 

 of ancestral characters, as the case may be. 



All such action is but ' heredity ' acting in one or other 

 mode; but there is another and fundamentally different 

 action which has to be considered, and that is the action 

 of the environment upon nascent organisms — an action 

 exercised either directly upon them, or indirectly upon 

 them through its direct action upon their parents. That 

 such actions produce unmistakable effects is notorious. It 

 will be, I think, sufiicient here to advert to such cases as 

 the well-known brood-mare covered by a quagga, and the 

 peculiar effects of a well-bred bitch being hned by a mongrel. 

 These show how an action exercised upon the female parent 

 (but \vith no direct action on the immediate offspring) may 

 act indirectly upon her subsequent progeny. 



As a rule, modifications accidentally or artificially induced 

 in parents are not transmitted to their offspring, as is well 



^ Mr Darwin tells us that two topknotted canaries produce bald offspring, 

 due probably to some conflicting actions analogous to the interference of light. 



