2l6 MARINE BIOLOGICAL LABORATORY. 



the nerve supply has been excluded from its just share 

 in forming the conclusions. 



These canal structures had no special phylogenetic 

 significance 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 persistently applied to the elucidation of Cyclo- 

 stome 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 necessity 

 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 recognize the 

 manner in which the structure and functions of organs 

 may be profoundly changed in the course of time. 



Now, while it is not known that Amphioxus is pro- 

 vided with an organ of hearing, the next higher forms 

 do possess an internal ear of such structure that not 

 only does it help us to understand the more complex 



