32 Heredity. 



that of an animal about to seize his prey. There will therefore be 

 a visual impression, a tension of the muscles : the latter condition 

 allows the animal either to seize a small object, if close to it, to 

 retire into its shell, or to escape from an enemy by convulsive 

 movements. 



Let us go further, and suppose a further development of the 

 animal's eyes, and a habit of moving about in the water. Of all 

 the bodies in its vicinity those in front of it commonly make the 

 strongest impression on it. These it first sees, and then often 

 touches ; and this contact often brings near to its head and its 

 tactile organs small bodies which nfsaL serve as food. The animal 

 will experience the recurring succession of these psychical con- 

 ditions : slight excitement of the retinal nerves ; excitement of 

 the nerves of the prehensile organs ; excitement of a special set 

 of muscles. These conditions must, by repetition in countless 

 generations, become so closely combined that the first will of 

 necessity call forth the others. 



' Here, then, we see how one of the simpler instincts will, under 

 the requisite conditions, be established by accumulated experiences. 

 Let it be granted that the more frequently psychical states occur 

 in a certain order, the stronger becomes their tendency to cohere 

 in that order, until they at last become inseparable ; let it be 

 granted that this tendency is, in however slight a degree, inherited, 

 so that, if the experiences remain the same each successive gen- 

 eration bequeaths a somewhat increased tendency ; and it follows 

 that, in cases like the one described, there must eventually result 

 an automatic connection of nervous actions, corresponding to the 

 external relations perpetually experienced. Similarly, if, from some 

 change in the environment of any species, its members are fre- 

 quently brought in contact with a relation having terms a little 

 more involved ; if the organization of the species is so far devel- 

 oped as to be impressible by these terms in close succession ; then 

 an inner relation corresponding to this new outer relation will 

 gradually be formed, and will in the end become organic. And 

 so on in subsequent stages of progress.' l 



It is, moreover, clear, as the author remarks, that we are not to 



1 Herbert Spencer, Principles of Psychology, 194 198, Second Edition. 



