82 

 Mustelas is not a true auiitory organ at all, but thit its 

 several parts are to be interpretei from the standpoint of the 

 equilibrium sense. The large nerve-tracts froro the ear to the 

 cerebellum are, therefore, iefinitely sii^nif icant, bein(5 the 

 connecting fibres between the central mechanism and its most 

 important peripheral organ. It also appears that not only 

 does the ontogeny of the ear show its relationship to the lat- 

 eral line organs, but the functions in the two instances are 

 comparable as well. 



An analysis of the habits of Viustelus will, it appears to 

 aie, go far towari explaining the disproportionately great devel- 

 opment of both the ear ^ni the cerebellum which we find the 

 animal to have. This shark, although a comparatively small 

 representative of the group, is, withal, a restless hunter of 

 the seas, ever urged onward by an appetite which, apparently, 

 has no bounds. Continually suspended in a fluid medium, and 

 compelled to balance itself at every turn, the animal requires 

 a precise mechanism of equilibration. This is to be found, in 

 the main, in both an ear and a cerebellum developed to a degree 

 out of all proportion to the scale occupied by the creature 

 as a whole. 



6. Evolution of the Cerebel lum. 

 6vidence of the origin of one brain-structare from another 

 is usually of tne most meager value, but it appears as though 



