130 DEVELOPEMENT OF THE NERVOUS SYSTEM. 



genenal system of nature. To accomplish this latter 

 purpose, we are provided with a system of organs, call- 

 ed organs of locomotion. 



Emily. Am I to understand that the latter are entire- 

 ly subservient to the former organs acting only when 

 stimulated by them ? 



Dr. B. Certainly ; no voluntary motion takes place 

 without the action of the nerves, but this view of the 

 subject must be considered at another time, for at pre- 

 sent we must look at the structure of the nervous system. 

 In order that you may obtain a clearer notion of this 

 system, we will first examine it in the inferior animals, 

 and thence trace it up into the nervous system of man. 

 In this manner, you will see in a very interesting light, 

 its gradual developement, and the relative importance of 

 its different parts. 



Emily. This system, like the others, I suppose, is 

 simple in the lower animals, increases in complexity as 

 we ascend the scale of being, and finally exists in its ut- 

 most perfection in man. 



Dr. B. Yes but its gradual developement differs 

 from that of the other organs, in one very remarkable 

 point. It is-^-that in the earliest stages of existence, it 

 is the same in all ; take it. in the highest state of perfec- 

 tion in which it is observed, and we find that before it 

 eould attain that state, it had to pass through all the forms 

 which it possessed in the different classes of inferior an- 

 imals in their perfect state. 



Jmi1y> If I understand your meaning correctly, the 

 nervous system of man, before it attains the form which 

 we behold, has first presented that of the zoophytes, 

 then that of the worms, then of the shell-fish, then of the 

 fishes, and so on through the whole series. 



Dr. B. Precisely so ; and now we will look at the 

 proofs of this doctrine. In the lowest orders of the 

 Zoophytes, the only trace of this system is nothing more 

 than nervous molecules unconnected with one another, 

 disseminated through the substance of their simple, pulpy 



