THE TRANSMUTATION OF SPECIES. 261 



of the organ to do the work demanded from it. It is, 

 moreover, certain that part passu with the change of 

 function of the great toe there would take place a 

 modification of its structure. It would gradually come 

 to be placed more and more at an open angle to the 

 other digits of the foot ; its muscles would become more 

 and more developed, giving it increased power and range 

 of movement ; an * opponent ' muscle might be developed ; 

 and, in all probability, the structure of the ankle would 

 become so far modified that the sole of the foot could 

 readily be turned inwards.* 



The above case is, of course, a purely imaginary one; 

 but there is nothing in it which would be inconsistent 

 with universally admitted biological laws. It is, however, 

 also strictly consistent with the Lamarckian theory; 

 since it affords an instance in which repeated efforts 

 on the part of the individuals of successive generations 

 to use a particular organ in a particular way would result 

 in the gradual change of that organ, both as regards 

 function and structure, so as to suit it to the new require- 

 ments (besoins) of the individual. 



As to the question how changes in the surrounding 

 conditions should give rise to corresponding changes in 

 the structures and organs of animals, Lamarck relied 

 principally upon the effects of use and disuse. No 

 doctrine in physiological science is better established 

 than that which teaches us that the habitual use of an 

 organ leads to a corresponding growth on the part of 

 the same. If we employ a particular muscle much, it 



* This power of inverting the sole of the foot is naturally possessed by the 

 young of the human species, as is also the power of freely moving the great toe, both 

 being more or less extensively lost in later life. 



