VL] n % Sitrtm rrf fod0gg. 107 



that it underwent a very curious change each fibre be- 

 coming shorter and thicker. By this act of contraction, 

 as it is termed, the parts to which the ends of the fibre 

 are attached are, of course, approximated ; and accord- 

 ing to the relations of their points of attachment to the 

 centres of motion of the different rings, the bending or 

 the extension of the tail results. Close observation of 

 the newly-opened lobster would soon show that all its 

 movements are due to the same cause the shortening 

 and thickening of these fleshy fibres, which are techni- 

 cally called muscles. 



Here, then, is a capital fact. The movements of the 

 lobster are due to muscular contractility. But why does 

 a muscle contract at one time and not at another ? Why 

 does one whole group of muscles contract when the 

 lobster wishes to extend his tail, and another group 

 when he desires to bend it ? What is it originates, 

 directs, and controls the motive power ? 



Experiment, the great instrument for the ascertain- 

 ment of truth in physical science, answers this question 

 for us. In the head of the lobster there lies a small 

 mass of that peculiar tissue which is known as nervous 

 substance. Cords of similar matter connect this brain 

 of the lobster, directly or indirectly, with the muscles. 

 Now, if these communicating cords are cut, the brain 

 remaining entire, the power of exerting what we call 

 voluntary motion in the parts below the section is de- 

 stroyed ; and on the other hand, if, the cords remaining 

 entire, the brain mass be destroyed, the same voluntary 

 mobility is equally lost. Whence the inevitable conclu- 

 sion is, that the power of originating these motions resides 

 in the brain, and is propagated along the nervous cords. 



In the higher animals the phsenomena which attend 

 this transmission have been investigated, and the exer- 

 tion of the peculiar energy which resides in the nerves 



