112 THE ASCENT OF MAN 



now be propagated, and the new uses for sound 

 itself, a more delicate instrument was required. And 

 hence one of the first things attended to as the 

 evolution went on was the construction and im- 

 provement of the ear. And this seems to have 

 been mainly effected by a series of remarkable 

 developments of one of the now superfluous gill- 

 slits. 



It has long been a growing certainty to Com- 

 parative Anatomy that the external and middle 

 ear in Man are simply a development, an im- 

 proved edition, of the first gill-cleft and its sur- 

 rounding parts. The tympano-Eustachian passage 

 is the homologue or counterpart of the spiracle 

 associated in the shark with the first gill-opening. 

 Prof. His of Leipsic has worked out the whole de- 

 velopment in minute detail, and conclusively demon- 

 strated the mode of origin of the external ear from 

 the coalescence of six rounded tubercles surround- 

 ing the first branchial cleft at an early period of 

 embryonic life.^ 



^ Haeckel has given an earlier account of the process in 

 the following words : — " All the essential parts of the middle 

 ear — the tympanic membrane, tympanic cavity, and Eustachian 

 tube— develop from the first gill- opening with its surrounding 

 parts, which in the Primitive Fishes (Selachii) remains through- 

 out life as an open blow-hole, situated between the first and 

 second gill-arches. In the embryos of higher Vertebrates it 



