No. I.] THE VERTEBRATE EAR. 153 



the division of a pore. Lips grow tipward and inward from the 

 edges of the pit, and, meeting above the organ, form a short sec- 

 tion of canal, the openings of wJiicJi are inclined to the general 

 surface, and give to the canal a tiuinel-like appearance. A nar- 

 row shallow channel, pigmented like the rest of the outer sur- 

 face, has meantime formed between the organs along the bottom 

 of the general depression. It is deepest near the newly formed 

 section of canal ; and into it the canal opens, the sides of the 

 openings passing gradually into the walls of the channel. The 

 limits of the canal are clearly defined by a sharp change in 

 direction of the bottom of the channel, the canal leading in- 

 ward at something of an angle, the walls of the canals and pits 

 always being much lighter in color than the outer surface. Tlie 

 openings of these short sections of canal may be called Jialf pores, 

 because, with a few exceptions, all the primary pores in the devel- 

 oped system are formed by the fusion of tzvo of them [italics 

 mine]. After its formation the short canal increases in length 

 by the continued coalescing of tJie edges of tJie eJiannel immedi- 

 ately beyond it, and the two Jialfpores are pushed apart along the 

 line of the canal toward other pores, zvhich are in a similar way 

 approaching thejn from adjoining sections. This process in Amia 

 is continued until the pores meet and unite, thus forming a con- 

 tinuous canal with a primary pore and tube between every two 

 consecutive organs ; but it may be arrested, in which case an 

 interrupted canal will be formed. At each end of a continuous 

 canal formed in this manner it is evident there must be a pore, 

 which, if it cannot unite with a pore of some other line to form 

 a double system, must always remain a half-pore or terminal 

 opening. 



"These two processes are continuous and essentially similar; 

 for even in the adult, two pores if forced together from want of 

 space, fuse." 



The little that is known of the development of the canals and 

 their organs in the bony fishes agrees essentially with this ac- 

 count of their development, but we have no such complete 

 history of canal development among other ichthyopsoid types. 



Let us now turn to the embryology of the vertebrate auditory 

 organs and examine the facts which have been accumulating for 

 many years, contributed from many different sources. Some 

 of the conclusions now accepted will doubtless change in time. 



