12 



effects being observed (amongst the members of the 

 organic world) from conditions which we assume to be 

 co-ordinate, but which in fact are not so; we may, on 

 the other, run a similar risk (and thus fail to discern a 

 corresponding modus operandi in the maturation of like 

 results), from a mere a priori belief that the lower 

 animals cannot be acted upon, by external influences, in 

 a manner at all equivalent to that which is self-evident 

 in the higher ones. 



" To make a perfect observer in any department of 

 science," writes Sir John Herschel, "an extensive ac- 

 quaintance is requisite, not only with the particular 

 science to which his observations relate, but with every 

 branch of knowledge which may enable him to appre- 

 ciate and neutralize the effect of extraneous disturbing 

 causes. Thus furnished, he will be prepared to seize on 

 any of those minute indications which often connect 

 phenomena which seem quite remote from each other. 

 He will have his eyes as it were opened, that they may 

 be struck at once with any occurrence which, according 

 to received theories, ought not to happen ; for these are 

 the facts which serve as clews to new discoveries *." 



There can be no doubt that amongst a large proportion 

 of our naturalists, differences, as such, are too exclusively 

 studied. Essential as their investigation is (for we could 

 not progress a step without some presumptive notion as 

 to the specific identity, or not, of the objects about which 



* Preliminary Discourse on the Study of Natural Philosophy 

 (London, 1830), p. 132. 



