2IO AYERS. [Vol. VI. 



The nerve end organs of the human ear are six in number. 



1. Macula acustica recessus utriculi. 



2. Crista acustica ampuUse anterioris. 



3. Crista acustica ampullae externalis. 



4. Crista acustica ampullae posterioris. 



5. Macula acustica sacculi. 



6. The mammalian cochlear organ, or Corti's organ. 



The two nerve end organs possessed by most all Vertebrates 

 from the fish up to Mammals are thus seen to be wanting in 

 these latter, — viz. macula acustica neglecta and papilla acustica 

 lagenae cochleae,^ — while the important sense organ of the 

 cochlea of Saurians has disappeared in the adult, though fully- 

 developed in the embryo, and functionally perfected before the 

 completion of Corti's organ, which supplants it. 



E. Phylogenetic Considerations. 



" Ich sagte, es sei mir gelungen, einen Grundplan des Gehororganes der Wirbel- 

 thiere, das Wesen des Baues desselben festzustellen. Dieser einfache Plan muss nun 

 nach dem grossen in die Wissenschaft eingefiihrten Principe wenigstens annaherungs- 

 weise am meisten in der niedersten Wirbelthierclasse hervortreten und sich zugleich 

 auf das strengste an die jiingsten Entwicklungsformen des Organes bei den Wirbel- 

 thieren xiberhaupt anschliessen " (Hasse, 1873). 



After an examination of all the evidence bearing on this 

 question, both from the embryological and the anatomical sides, 

 I propose the following solution of the problem of the mor- 

 phological value of the parts of the internal ear and their inter- 

 relationships. I believe there can be no doubt that the in- 

 ternal ear develops from superficial canal organs, and this belief 

 has led me to the discovery of the very simple law which governs 

 their origin and succession. Stated in few words their origin 

 and sequential relations are as follows : — 



The primitive auditory sense organ is invaginated from the 

 surface of the body, and may be said at this time to be in the 

 vesicular stage (Cut 25, A). So far as we know, this condition 

 is not retained by any adult living vertebrate. And it is quite 

 possible that the auditory saucer may contain the rudiments of 



^ The papilla acustica basilaris has also disappeared as such, and is represented by 

 only one of its descendants, the organ of Corti. 



