THE EAR OF MAN. 213 



a manner that the smaller sense-organ appears as a bud 

 from the parent. There are thus formed within the 

 two chambers of the ear four canal sense-organs be- 

 longing to the third generation. The two external 

 organs are soon enclosed within the ampulla of two 

 complete and relatively large canals, which are now 

 formed about them. An anterior vertical and a pos- 

 terior vertical formed in the manner already fully de- 

 scribed. Up to this time the organs have retained the 

 primitive relations to each other — a serial arrange- 

 ment along a line running in an antero-posterior direc- 

 tion. Now, there begins a distortion of the structure 

 as a whole, which continues ever after, and reaches 

 its greatest development in the mammals — viz. a pro- 

 cess of sinking and drawing out ventrally of the 

 posterior chamber of the ear, so that hereafter we 

 might speak of a superior and an inferior portions or 

 chambers. The sense-organs of the third generation 

 play the leading role in these changes, and by means 

 of four sets of divisions, viz. by the bipartition of each 

 sense-organ present in the Cyclostome stage nearly 

 simultaneously there is produced a fourth generation 

 of canal sense-organs. 



To this fourth generation belong all the sense-organs 

 of the internal ear of the higher vertebrates which in 

 the diagram are numbered eight to fifteen consecutively. 



During this process of sense-organ differentiation, 

 the canals have been variously modified, and to show the 

 relationship of the third generation to the fourth let us 

 examine the diagram shown in Fig. 15, in the construc- 

 tion of which I have ignored the ventral distortion 

 spoken of. 



