2i6 AV£/?S. [Vol. VI. 



liarities are to be regarded as primitive or as the result of 

 degeneration. The much greater simplification of the ear in 

 Myxine suggests strongly of degeneracy, but, on the other 

 hand, the entire absence of the horizontal semicircular canal 

 may very well be a primitive feature. It is plain that the audi- 

 tory organ of the Lamprey is derived from the same primitive 

 type as that of the higher vertebrates ; but whether in the 

 differentiation of the Lamprey it has passed through stages 

 higher than the present condition, and more like that of the 

 typical fishes, cannot from present evidence be decided." 



" Regarded as a whole, the sense organs of Petromyzon do 

 not show degeneracy, but rather a retardation of development." 

 As this quotation shows, Scott was well satisfied from his 

 studies of the development of the Lamprey that it could not 

 have descended from more highly organized ancestors, but he 

 was not able to decide what relationship (to descend to partic- 

 ulars) the ear of Myxine bears to that of Petromyzon, nor the 

 genetic connections of the Cyclostome ear with the higher fish 

 type. 



Scott's conclusion (loc. cit. 300) that " the epidermal sense 

 organs of the head and the lateral line are not developed in con- 

 nection with the ganglia of the cerebral nerves, or with the 

 lateral nerves, but at a later stage " has been shown by Kupffer • 

 to be erroneous. And the light which the latter's researches 

 have thrown upon the relation of the superficial sense organs 

 to ganglion formation on the one hand, and to the internal ear 

 on the other hand, is most welcome and important. 



The walls of auditory vesicle are converted only in part into 

 the labyrinth of the ear, the other part forming a ganglion ; and 

 since the relations of the invaginations in connection with the 

 ganglia of the V and X nerves bear the same relation to 

 these ganglia that the auditory involution does to the acustico- 

 facial ganglia, and since we know the latter to be an involution 

 of an organ of the lateral line system of canal organs, it follows 

 that all these invaginations are intimately connected with pro- 

 duction of the sense organs of this system. That the canals 

 are not found in the Cyclostomes, save in the case of the audi- 

 tory organs, is due to a secondary modification of the process of 

 development ; the process of canal formation going no further 

 than the primitive invagination, which soon disappears. 



