No. I.] THE VERTEBRATE EAR. 317 



Recapitiilatio7i E. 



29. The vertebrate ear is a relatively late acquisition, phylo- 

 genetically speaking, and among the Sauropsida and Mammalia 

 it offers the only remnant of the canal organs of their ichthyopsid 

 ancestors. 



30. The outcome of the survey of the anatomical and embryo- 

 logical fields is the conclusion that the surface territory out of 

 which the ear developed was the best offered by the anatomical 

 conditions of the ancestors of present vertebrates, and that the 

 superiority of the territory chosen by natural selection over 

 any other portion of the surface of the body lay in its combin- 

 ing in small space two, and that differently innervated, sensory 

 apparatuses of a kind suitable for the further perfection of the 

 function of the perception of wave motion. Among the higher 

 forms the semicircular canals are degenerating, and one canal 

 organ, the crista abortiva, has entirely disappeared. Corti's 

 organ is not the papilla basilaris, as Retzius concludes, in agree- 

 ment with Hasse and other anatomists, but only a small portion 

 of it which has undergone peculiar modifications. 



31. The auditory organs of invertebrates are not the forerun- 

 ners or the ancestral forms of the vertebrate auditory organs, 

 but they are differentiated structures which are confined strictly 

 to the invertebrate group. It is of course possible that other 

 sense organs of the invertebrate body have developed in the 

 course of descent into the canal organs from which the verte- 

 brate ear arose, but on this topic I have nothing to add to the 

 opinions already expressed by other investigators. 



Recapitidatio7i F. 



32. The functions of the ampullar sense organs and their 

 connected canals can hardly be different from the sense organs 

 of the lateral line, except in refinement of function ; i.e. the 

 difference can only be one of degree and not of kind. The 

 highly modified line of cochlear organs has certainly carried 

 the refinement of function much further, but it is not indicated 

 anywhere that a different kind of function has been added to 

 or substituted for the ancestral function. 



The careful comparative study of the internal ear in its rela- 



