Characters, Hereditary and Acquired. 71 



ordinated parts, must somehow or other be originated 

 in a high degree of working efficiency, before it can 

 be capable of answering its purpose in the prompt 

 performance of a particular action under particular 

 circumstances of stimulation. Lastly, such pieces of 

 machinery are always of a highly delicate character, 

 and usually involve so immensely complex a co- 

 ordination of mutually dependent parts, that it is only 

 a physiologist who can fully appreciate the magnitude 

 of the distinction between "adaptations'" of this kind, 

 and *■ adaptations " of the kind which arise through 

 natural selection seizing upon congenital variations as 

 these oscillate round a specific mean. 



Or the whole argument maybe presented in another 

 form, under three different headings, thus : — 



In the first place, it will be evident from what has 

 just been said, that such a piece of machinery as is con- 

 cerned in even the simplest reflex action cannot have 

 occurred in any considerable number of individuals 

 of a species, when it first began to be constructed. 

 On the contrary, if its origin were dependent on con- 

 genital variations alone, the needful co-adaptation of 

 parts which it requires can scarcely have happened to 

 occur in more than a very small percentage of cases — 

 even if it be held conceivable that by such means 

 alone it should ever have occurred at all. Hence, 

 instead of preservation and subsequent improvement 

 having taken place /« consequence of free intercrossing 

 among all individuals of the species (as in the cases 

 of protective colouring, &c., where adaptation has.no 

 reference to any mechanical co-adaptation of parts), 

 they must have taken place in spite of such inter- 

 crossing. 



