No. I.] THE VERTEBRATE EAR. 307 



and cristae acusticas of the ear. The deep-seated existence of 

 this belief is very impressively illustrated by the fact that when 

 new facts have been discovered in the anatomy of the ear organs 

 they have been found to be true of the canal organs, and vice 

 versa. Likewise, the errors in our knowledge were common to 

 both. The ontogeny of the ear has disclosed many new facts, 

 and as fast as the ontogeny of the canal organs has been worked 

 out they have been found to agree in the details of their ontog- 

 eny with the ear canal organs no less than in their adult 

 anatomy. 



The processes which I have described in the chapter dealing 

 with the development of the ear canal complex were not known 

 to occur in the development of the lateral line canals, and von 

 Noorden's circumstantial account of the formation of the cristae 

 acusticas and their ampullae and canals remained, like all previous 

 accounts of ear anatomy and development, a series of dry facts, 

 until leavened by the addition of Allis's germinal series of facts 

 concerning the development of the surface sense organs and 

 their canals. Then the slumbering idea, already a century old, 

 arose in a concrete demonstrable form and became clothed in 

 a garment of facts logically arranged and consequently easily 

 grasped and understood. Indeed, so easily grasped, that al- 

 ready, before all the details are worked out, we have forgotten 

 that there was any difficulty or uncertainty about the demon- 

 stration of the old, half-perceived idea, which was so uncertain 

 in form that men were not quite sure that all this homology 

 might not be mere parallelism. 



2. In describing the Elasmobranch ear I have emphasized 

 the necessity of keeping in mind the relation of the chambers 

 and channels of the internal ear to each other as that of a com- 

 plexus of surface sense organ canals sunk below the surface of 

 the head with the dermal surface (from which the canals are 

 generated), as the lining of the main chambers — the two co- 

 ordinate and primary chambers of the ear. It was found that 

 in Dasyatis the ear presents a remarkably symmetrical arrange- 

 ment of parts which, taken as a typical form, permits of the 

 union of all vertebrates according to a simple and logical plan 

 of development (so far as the ear is concerned), and satisfies as 

 well all the demands yet made by any anatomical facts, for the 

 derivation of the ear from pre-existing surface canal organs. 



