LIMITS OF NATURAL SELECTION. 17 



have their orderly psychical correlatives? We see 

 the brain going through successive changes of 

 shape and structure until it arrives at such a 

 stage in the new-born animal that it is capable of 

 directing highly complex instinctive actions. At 

 what point in this succession of changes does the 

 psychical element appear ? can we imagine it as 

 suddenly arising in the brain as the new-born creat- 

 ure draws its first breath ? If instinct be correlated 

 with certain material structures of the brain, as 

 we have reason to believe, can we suppose that 

 those structures have been produced by a method 

 of development totally different from that of all 

 the other organs. The general course of develop- 

 ment of any organ is from the simple to the com- 

 plex ; and the development of the organ in the 

 individual is a repetition of the development of the 

 organ in the race. Thus it seems probable that 

 a bird, which, at one period of its embryonic devel- 

 opment, with its gill-clefts and unjointed rudiment- 

 ary limbs, so strongly resembles a fish, should 

 also have passed through a stage of brain devel- 

 opment or a potential psychical condition some- 

 what similar to that stage at which the fishes have 

 remained. So far as may be judged by the appear- 

 ance of the brain, we may conclude that such a 

 stage has been passed through by the bird, for 



