13S on w-orms, Marc^ 28. 



is vain to inquire into tlie nature of the sentient 

 principle, before we know the structure and functions 

 of the organs of sensation. 



Permit me, then, for my own information, to state 

 a few facts, and to put a few questions respecting the 

 organs and the seat of sensation, as they appear in 

 certain clafses of animals. In men, and in the higher 

 orders of animals, we all know that sensation centers 

 in the brain ; that it is propagated by motion from 

 the extremities of the nerves ; and that the sentient 

 principle, whatever it be, cannot be divided. The 

 facts, from which these conclusions are drawn, it is 

 necdlefs for me to enumerate. Every one, who has 

 at all studied the subject, has had sufficient evidence, 

 that sensibility, and tlie power of motion, are by the 

 nerves conveyed to all parts of the body from the 

 brain and spinal marrow ; that when the nerves of 

 any part are cut, tied, or strongly comprefsed, the 

 functions of that part are either destroyed or much 

 impaired •, and that, when a great injury is done to 

 the medullary substance of the brain itself, sensa- 

 tion, memory, and intellect, are wholly lost. But in 

 •worms, and in certain species of insects, the faculty 

 ©f sensation exhibits a very different apj>earance. If 

 gin earth-worm be cut in two pieces, sensation, so far 

 from being lost, remains as well with the tail as with 

 the head ; and„ which is yet more wonderful, each 

 piece, instead of instantly dying, becomes, in time, a 

 complete worm. This power of reproduction, however, 

 appears to be subject to certain laws. " Having found," 

 e.iys jibbt Spallanzani, <' that the anterior part, or the 

 hpad, reproduced the tail. I wa-s willing to try whe- 



