THE ORIGIN OF NERVES. 295 



named the " membranous labyrinth " of the ear. The lower 

 part (c) of this sac becomes the " cochlea " of the ear, the 

 other part forming the " semicircular canals" (/). The " audi- 

 tory nerve " (n), or that of hearing, appears to be formed 

 on the inner side of the labyrinth (/), and thus places the 

 ear in communication with the brain. 



It may thus be said that the ear-structures are more largely 

 indebted for formation to the skin-layer than are those of the 

 eye ; since no outgrowth from the brain comparable to that 

 seen in the case of the eye takes place in the development 

 of the ear. Be this as it may, however, there remains the 

 fact that the most important of our sensory organs, eye, ear, 

 and nose, with the intricate structural relationships they 

 evince in the adult animal, are not originally formed within 

 the body, but are developed from the outermost or skin- 

 tissues of the young animal, and are placed thereafter in 

 connection with the brain, which itself, as we have seen, was 

 developed from the same outward layer so distinctly to be 

 discerned in the earliest stages of life. What, then, are the 

 inferences concerning the origin of nerves which may be 

 reasonably drawn from the story which development not 

 merely tells, but substantiates by the plainest of evidence ? 

 Simply, that our nervous centres and sense-organs, by means 

 of which we not merely feel, see, and hear, but through 

 which we exercise the highest powers of will, reason, and 

 intelligence, are formed from a layer which originally, and in 

 antecedent states of existence, met the rough and direct con- 

 tact of the outer world. Through the scientific use of the 

 imagination we note that as time passed, and as development 

 advanced, with its wondrous work of evolving and fashioning 

 new forms out of the old, the nervous system gradually rose 

 in complexity. From the condition of a soft contractile 

 body, typified by the amoeba, and subject at each and every 

 part of its surface to receive impulses, we reach a stage 

 wherein a stable shape of body presented certain points for 

 the reception of sensations in preference to other portions. 

 Then, as in the medusa, a defined communication between 



