No. I.] THE VERTEBRATE EAR. 213 



The sense organ numbered 4 of the Cyclostome stage (the 

 macula utricuh of Myxine and Petromyzon) divides into the 

 sense organ 8 and sense organ complex 14 of the Gnathostome 

 stage, the macula utriculi of the human ear, which is, as I 

 stated when describing the Torpedo ear, a compound organ 

 composed of the parent organ and its numerous progeny, all 

 of which remain close together. 



The sense organ numbered 7 of the Cyclostome stage is 

 the sense organ of the posterior canal of Myxine and Petromy- 

 zon, and has divided to produce sense organs 11 and 13 of the 

 Gnathostome stage, or the crista acustica posterioris, or the 

 canal sense organs of the posterior canal of the human ear, 

 and the so-called macula acustica neglecta of Retzius, which 

 is the abortive second horizontal canal organ of the internal 

 ear of man. 



Sense organ 5 of the Cyclostome stage has divided to pro- 

 duce the sense organ 9, and the sense organ complex 15 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 generalization which we owe to 

 Beard, but which he did not attempt to establish by any detailed 

 anatomica or embryological investigations, the phylogenesis of 

 the vertebrate 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 vesicle have been used 

 alone as the basis for proofs of the genetic connection of the 

 types of internal ear — even the nerve supply has been excluded 

 from its just share in forming the conclusions generally accepted 

 hitherto. 



The following table gives the genetic relation of the several 

 sense organs of the ear, the group of animals in which each 

 organ made its appearance, the length of time it persisted or 

 whether it still persists, measured in terms of geological time, 

 the fluctuations undergone by organs during their term of exist- 

 ence, whether of increase or decrease, and the time of death 

 together with the group suffering such loss. In the case of 

 the papilla basilaris, although it rises in the Reptilia into the 



^ See Recapitulation D. 



