THE HISTORY OF MENTAL DEVELOPMENT 131 



most of the actions of the body will go on better with- 

 out its interference. It is not yet sufficiently de- 

 veloped, or, so to speak, wise enough to be intrusted 

 with rnuch control of the animal. 



Among higher worms cases of instinct seem proven. 

 Traces of it will almost certainly be yet found much 

 lower down. Fresh-water mussels migrate into deeper 

 water at the approach of cold weather. And if the 

 clam has instincts, there is no reason why the turbel- 

 laria should not also possess them. But all higher 

 powers develop gradually, and their beginnings usually 

 elude our search. Along the line leading from an- 

 nelids to insects instinct is becoming dominant. A 

 supraoesophageal ganglion has developed, and has been 

 relieved of most of the direct control of the muscles. 

 Very good sense-organs are also present. From this 

 time on consciousness becomes clearer, and the brain 

 is beginning to assert its right to at least know what 

 is going on in the body, and to have something to say 

 about it. Still, as long as the actions remain purely 

 instinctive the brain, while conscious, is governed by 

 heredity. The animal does as its ancestors always 

 have. It does not occur to it to ask why it should do 

 thus or otherwise, or whether other means would be 

 better fitted to the end in view. It acts exactly like 

 most of the members of our great political and theo- 

 logical parties. And until the animal has a better 

 brain this is its best course and is favored by natural 

 selection. 



But the hand of even the best dead ancestors cannot 

 always be allowed to hold the helm. The brain is 

 still enlarging, the sense-organs bring in fuller and 

 more definite reports of a wider environment. Greater 



