No. I.] THE VERTEBRATE EAR. 89 



condition they easily break away en masse, or stick to the walls. 

 Hensen concluded that the hairs of the Frog end more pointedly 

 than those of fishes, but that they also have heavier bases, with 

 more sharply defined structural detail. Hensen confirms Ret- 

 zius's discovery that the so-called hair from a cell is composed 

 of many finer fibrillae. In optical cross-section one is able to 

 determine that the number of fibres which enter into the body 

 of a round hair is about eighteen to twenty. The thickness of 

 a single fibre is 0.0007 mm. Hensen found that in some species 

 of Teleosts, if the ampulla was disturbed before killing and 

 fixing with osmic, no cupula was formed. It was invariably 

 present when the ampulla was hardened in osmic in sihi. In 

 other species the ampullae would bear removal, and still give 

 good cupulae. 



When such osmic cupulae were hardened in Miiller's solution, 

 for twelve hours after fixing, it was found that they remained 

 firmly fixed to the crista, contrary to the observations of other 

 authors, with respect to lack of attachment of the cupula to 

 the crista. 



Hensen was enabled to observe the various stages of the 

 formation of the cupula by the action of reagents, and to prove 

 conclusively that it was gradually formed from the hairs or from 

 the intercapillary substance. He was inclined to think that the 

 latter matter was the source of the artifact and that the hairs 

 projected up into it or were more or less bent outward before 

 entering the gelatinous mass. The cupula of osmic acid is much 

 different from the chromic acid structure (Kuhn's), or from the 

 hydrochloric acid cupula (Lang's). 



Retzius (1884, 237, II) gives up his former position, after a 

 careful study of the problem, admits the truth of Hensen's 

 position, but calls attention to the fact that the latter author 

 assumes the presence of an intercapillary substance whose coag- 

 ulation by reagents gives rise to the cupula, so that, as he 

 thinks, Hensen really assumes the presence of a sort of fluid 

 cupula after all. Although loath to give up his former views 

 entirely, resting as they did on many carefully prepared ears and 

 on their careful study both by himself and his friends, Retzius 

 does so since he had observed the degrees of cupula formation. 



My own observations lead me to deny the presence of a 

 special intercapillary substance anywhere in the ear. 



