2i8 AVERS. [Vol. VI. 



group, which, so far as existing forms are concerned, is a very- 

 small one. 



With the Elasmobranchs appear the third canal organ and its 

 canal, the so-called horizontal, external or lateral canal. We 

 know from the development that its sense organ arose by the 

 division of the crista acustica ampullae anterioris of the Cyclo- 

 stome type. We are also in position to say that the older view 

 advocated by morphologists, that the two verticals are the older, 

 and the horizontal the younger canal, is the true one, while 

 the view advanced recently by Villy is entirely erroneous — the 

 reverse of the truth, and rests not upon a fundamental fact of 

 development, but upon a variation, an ontogenetic departure 

 from phylogenesis, such as not infrequently occurs in the de- 

 velopment of all organs, especially in the higher animals. 



Against the view that the completed canal of the canal sys- 

 tem is the primitive condition of the system, so far as existing 

 vertebrates are concerned, one may oppose the very plausible 

 objection that, since all of the Holocephala and some Teleosts 

 have the canal incomplete as a more or less open groove on the 

 surface of the body, and since the Cyclostomes do not retain 

 the canals in any form during adult life, and further, since the 

 closed canal may be easily formed by the fusion of the borders 

 of such open grooves as are present in, e.g. Chimaera, and 

 Tetrodon, 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 type 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 inclosed in complete canals by a 

 process exactly similar to that discovered in the formation of the 

 sense organs and their canals in the admittedly primitive ganoid 

 type, we are compelled to admit that such a process could 

 hardly have arisen within the closed capsule after its separation 

 from the surface and its removal away from external influences, 

 and that consequently there must be a genetic relationship 

 between the canal organs of the internal ear and the superficial 

 canal organs ; and since there is not the slightest doubt that 

 the superficial canal organs are the original or parent organs, 

 we are brought to the unavoidable conclusion that the vertebrate 

 ear is a transformed canal organ. By the involution of the 



