THE EAR OF MAN. 21/ 



Gnathostome type, but proves conclusively that, so far 

 as the ear is concerned, the Cyclostomes have not suf- 

 fered degradation of structure. 



Against the view that the completely closed or perfect 

 canal is the primitive condition of this system, so far as 

 existing vertebrates are concer7ied, one may raise the very 

 plausible objection that since all the Holocephala and 

 some Teleosts have the canal incompletely developed, as 

 a more or less open groove on the surface of the body, 

 and since the Cyclostomes do not retain the superficial 

 canals except in very imperfect form during adult life, 

 and further, since the closed canal is produced in 

 ontogeny, and may have appeared in phylogenetic his- 

 tory by the action of the same process,^ it is only 

 reasonable to suppose that the open groove is the 

 primitive condition, and constitutes a phylogenetic stage 

 passed through in the development of the higher (?) 

 types of closed canal. 



When, however, we consider that the internal ear is a 

 very ancient structure, and that in all known cases the 

 sense-organs developed in it become enclosed in com- 

 plete canals, by a process exactly similar to that known 

 for the formation of the superficial canal organs and 

 their canals in the admittedly primitive ganoid type, we 

 are compelled to admit that such a process could hardly 

 have arisen independently within the closed capsule 

 after its separation from the surface and its removal 

 away from the external influences which originally 

 caused their development, and that consequently there 



^ e.g. the grooves present on the surface of the head and body of Chi- 

 mcera and Tetrodons, could readily be converted into tubes by the fusion 

 of their edges. 



