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 may be 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 in 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. 



