2l8 MARINE BIOLOGICAL LABORATORY. 



imist be a genetic relationship between the canal organs 

 of the internal ear and tJie superficial canal organs ; and 

 since there is not the sUghtest doubt that the super- 

 ficial canal organs are the original or parent organs, we 

 are brouo^ht to the unavoidable conclusion that the ver- 

 tebrate intertial ear is a transformed canal organ. 



It follows from what I have said that the system of 

 canal sense-organs must be a very ancient one, since it 

 must have antedated the origin of the internal ear of 

 the Cyclostomes. 



Although ontogenetic evidence seems to lead to the 

 conclusion that the auditory organ arose by the in- 

 vagination of a single superficial sense-07gan, it is by 

 no means certain that this is true ; for there are certain 

 facts of comparative anatomy and certain phylogenetic 

 considerations which point to the conclusion that the 

 auditory organ has arisen by the bringing together of 

 two originally distinct sense-organs which were together 

 sunk below the surface. The main facts at present in 

 favor of this view are these : — 



1. In all eared vertebrates the auditory organ is sup- 

 plied from two distinct brain centres, one lying in close 

 connection with the facial nuclei, the other intimately 

 related with the glossopharyngeal nucleus. 



2. In all eared vertebrates the so-called auditory 

 nerve is composed of two distinct roots — an anterior 

 and a posterior — which supply the anterior and pos- 

 terior chambers respectively. 



3. In all these forms the anterior root is external 

 to the brain, united with the facial nerve. 



4. In some fishes the nerve to the posterior ampulla 

 is derived from the glossopharyngeal nerve, between 



