THE EAR OF MAN. 21 5 



The sense-organ numbered four of the Cyclostome 

 stage (the macula utriculi of Myxine and Petromyzofi) 

 divides into the sense-organ eight and sense-organ com- 

 plex fourteen of the Gnathostome stage, the macula 

 utriculi of the human ear, which is, as I stated when 

 describing the Torpedo ear, a compound organ com- 

 posed of the parent organ and its numerous progeny, 

 all of which remain close together. 



The sense-organ numbered seven of the Cyclostome 

 stage is the sense-organ of the posterior canal of Myxine 

 and PeU'oinyzon^ and has divided to produce sense- 

 organs, eleven and thirteen, of the Gnathostome stage, 

 or the crista acustica posterior, or the canal sense-organ 

 of the posterior canal of the human ear, and the so-called 

 macula acustica 7ieglecta of Retzius, which is the abortive 

 second horizontal canal organ of the internal ear of man. 



Sense-organ five of the Cyclostome stage has divided 

 to produce the sense-organ nine, and the sense-organ 

 complex fifteen of the Gnathostome stage, or the macula 

 sacculi and the lagenar organ respectively, the organ of 

 Corti of the human ear. 



With the exception of the generalization that the 

 vertebrate internal ear is derived from branchial sense- 

 organs — i.e. organs of the lateral line system — a gen- 

 eralization which we owe to Beard, but which he did not 

 attempt to establish by any detailed anatomical or em- 

 bryological investigations, the phylogenesis of the ver- 

 tebrate ear has been studied only on the basis of the 

 adult structure. Such structures as the semicircular 

 canals and the divisions of the body of the auditory ves- 

 icle have been used alone as the basis for proofs of the 

 genetic connection of the types of internal ear — even 



