32 DARWINISM AND EVOLUTION. 



THE NERVOUS SYSTEM. 



"VTow the evolution of a nervous system is a necessary con- 

 -*-^ comitant of that specialisation which originates the senses. 

 On the one hand, until the general sensitiveness is in some degree 

 localised, the internuncial function (the telegraph office) of the 

 nervous system cannot exist ; and on the other hand no such 

 localised sensitiveness can exist without something that answers to 

 nerves ; there must be a tract of least resistance along which 

 molecular vibrations flow. A nascent sense of sight, therefore, 

 implies a nascent nervous communication, and along with a 

 nascent nervous communication we may see the first illustration 

 of the growth of intelligence. 



If psychical states follow one another, time after time, in a 

 certain order, so as eventually to become inseparable ; then it 

 must happen that if, in the experience of any species, a visual 

 impression, a tactual impression and a contraction are continually 

 repeated in this succession, the several nervous or psychical states 

 produced will become so consolidated that the first cannot be 

 caused without the others following. There will thus occur a 

 contraction in anticipation of touch • ana 7 we see the origin of 

 reflex action. 



When vision is further developed, the same bodies will be 

 discovered at greater distances, and smaller bodies will be dis- 

 covered when close by. Both of these must produce obscurations 

 which are faint in comparison with that obscuration produced by 

 a large body about to strike the creature's surface. But now mark 

 the accompanying experience. A faint obscuration will not, like 

 an extreme one, be habitually followed by a strong tactual 

 impression and a subsequent contraction. If caused by a great 

 mass passing at some distance, there will probably be no collision 

 — no tactual impression at all. If caused by a little mass which 

 is very near, the collision that follows will be comparatively slight ; 

 so slight as not to cause a violent contraction, but only such 

 tension in the motor apparatus as is seen in any creature about to 

 seize upon its prey. 



