No. I.] THE VERTEBRATE EAR. 215 



Retzius finally came to the conclusion that this nerve end 

 organ had arisen from the posterior, ampullar sense organ, and 

 that among the higher forms, especially the Mammalia, it was 

 no longer produced, or, as he expressed it, the macula neglecta 

 in these forms had disappeared in the crista acustica posterior. 



These canal structures had no special phylogenetic signifi- 

 cance for investigators in this field ; for although it was known 

 that the auditory vesicle was invaginated from the surface of 

 the body, the connection of the sensory part of the invagination 

 with the superficial canal organs was not understood. Now 

 that we know that there is a genetic connection, many of the 

 intricate problems receive their solutions, and the genetic rela- 

 tionships appear clear and certain for all the types. The 

 demonstration of these facts deals another blow, and a fatal 

 one, at the degeneration hypothesis which has been so persist- 

 ently applied to the elucidation of Cyclostome anatomy and 

 development, with such pernicious morphological results. (This 

 will apply equally to Amphioxus, though only indirectly in this 

 particular instance.) This solution relieves us from the neces- 

 sity of explaining away the vertebrate ear on every occasion, 

 when we seek to establish a relationship between the vertebrate 

 and the invertebrate types ; for we are led to see the value of 

 very simple, superficial sense organs in an undifferentiated 

 group of animals, for the building up of structures of great 

 complexity, and of intricate relations to other parts of the 

 animal body in the members of higher forms, and also to recog- 

 nize the manner in which the structure and functions of organs 

 may be profoundly changed in the course of time. And it also 

 enables us to understand how a primitive central nervous sys- 

 tem like that of Amphioxus may be altered by the development, 

 the high specialization of circumscribed areas of the periphery 

 necessitating specialization of the central apparatus. 



Now, while it is not known that Amphioxus is provided with 

 an organ of hearing, the next higher forms do possess an inter- 

 nal ear of such structure that not only does it help us to 

 understand the more complex Gnathostome type, but proves 

 conclusively that, so far as the ear is concerned, the Cyclo- 

 stomes have not suffered degradation of structure. In his 

 paper on the development of Petromyzon, Scott (1887, 259), loc. 

 cit. p. 297, says : " It is a question as to whether these pecu- 



