so TIIK (JKNKSIS OF SPECIMS. [Ciiai'. 



Soleclion " onhj it is so iniprohable as to be practically im- 

 possible for two exactly-similar structures to have ever 

 been iudependently developed. It is so because the num- 

 ber of possible variations is indefinitely great, and it is 

 therefore an indefinitely great number to one against a 

 similar series of variations occurring and being similarly 

 preserved in any two independent instances. 



The dilliculty here asserted applies, however, only to 

 pure Darwinism, \vhich makes use only of indirect modifi- 

 cations through the survival of the fittest. 



Other theories (for example, that of Mr. Herbert Spen- 

 cer) admit the direct action of conditions upon animals and 

 j)lants — in ways not yet fully understood — there being con- 

 ccivcKJ to be at the same time a certain pc^culiar but limited 

 power of response and ada})tation in each animal and plant 

 so acted on. Such theories have not to contend against 

 the difhculty proposed, and it is here urged that even very 

 comj)lex extremely similar structures have again and again 

 been developed quite independently one of the other, and 

 this because the j)rocess has taktiu place not by meri;ly 

 haphazard, indefinite variations in all directions, but by tlie 

 concurrence of some other and internal natural law or laws 

 cooperating with external influences and with " Natural 

 Selection" in the evolution of organic forms. 



It must never be forgotten that to admit any sucli con- 

 stant operation of any such ludvuown natural cause is to 

 deny the purely Darwinian theory, which relies upon the 

 survival of the fittest by means of minute fortuitous indefi- 

 nite variations. 



Anumg many other obligations which the author has 

 to acknowledge to Prof. Huxley are, the pointing out of 

 this very dilliculty, and tlie calling his attention to the 

 striking resemblance between certain teeth of the dog and 

 of the thylacine as one instance, and certain ornithic pe- 

 culiarities of pterodactyls as another. 



