23 AYERS. [Vol. VI. 



than the alligator. The lowest mammals, Echidna and Orni- 

 thorhynchus, show most decided reptilian characteristics, and 

 they may be said with truth, I think, to possess a well-developed 

 lao-ena, or the Anlage of a cochlea, as well as the organ of 

 Corti. One great peculiarity of the cochlea is the spiral twist- 

 ing it has acquired during its phylogeny, and which is repeated 

 in each ontogeny. Since the cochlear sense organ originates 

 as a canal sense organ, and ifs adult condition is directly trace- 

 able from such primitive conditions, we must conclude that the 

 organ of Corti is a canal organ derivative, and that in the adult 

 condition it either represents a chain of sense organs closely 

 connected, or it is a single but much elongated organ. 

 • When one studies the condition of the sense organs of the 

 vertebrate ear, as found, for instance, in Torpedo and Dasyatis 

 (Cut I and PL I, Figs, i and 3), the equal division of nerve 

 end organs between the two branches of the auditory nerve, 

 the anterior and posterior respectively, is perhaps the most 

 fundamental and important relation presented. I am sure, how- 

 ever, that we cannot overestimate the fact that the ampullar 

 organs are here sharply divided into two groups, each group 

 communicating with its own division of the utriculo-sacculus, 

 the anterior consisting of a pair of ampullar organs formed by 

 the division of the anterior ampullar organ of the Cyclostome 

 type, the posterior remaining a single organ so far as the pro- 

 duction of an ampulla is concerned. Nor must the relation 

 escape us that the anterior group is connected with the utric- 

 ular organ, while the posterior group is as certainly connected 

 with the saccular organ. (See type figures, PI. IX, Figs. 2 

 and 3.) 



The ampullar sense organs not infrequently divide without 

 causing a division of the ampulla and canal, but in all such 

 cases we find the supernumerary organ still inclosed in the 

 ampulla with its parent, though supplied by a distinct branch of 

 the ampullar nerve. The offspring is usually removed a short 

 distance from the parent and may lie anywhere between the 

 utriculo-saccular chamber and the parent ampullar chamber. I 

 have seen as many as four sense organs in the course of a 

 single ampullar canal. 



