g8 AYERS. [Vol. VI. 



over many species of fishes and amphibia. He considered the 

 cupula to be a normal structural element of the vertebrate 

 ampulla, since he had always found it as a sharply defined and 

 regularly formed structure, on account of which he was unable 

 to accept Hensen's views, though he distinctly states that owing 

 to the fact that his observations had for the most part been 

 made before Hensen's article was published, he did not give 

 the latter that consideration which he now concedes was its 

 just due. He had never found the auditory hairs free and long 

 except in the case of Proteus, and this, to him, unusual condi- 

 tion he was entirely unable to explain in the light of the cupula 

 terminalis. 



Hensen (1881, 132) appeared again in print, denying in the 

 most emphatic manner the natural existence of the cupula 

 terminalis. He repeated his former observations and measure- 

 ments of the auditory hairs made on species of Gobius, this time 

 a younger fish, 10-30 mm. long, and arrived at the same results 

 as formerly. Concerning the relations of the otolith hairs to 

 the otoliths, he states that the latter are borne by the hairs 

 o.oi mm. from the surface of the epithelium. The small oto- 

 liths seem to be inclosed in a membrane, while the larger ones 

 lack the membranous envelope. The coverings of the maculas 

 utriculi and sacculi, Hensen could not find ; and so he declared 

 those described by various authors to be artifacts. 



The long auditory hairs of the ampullse of adult Teleosts may 

 be readily observed if the ampulla is carefully removed from the 

 head, and examined under slight pressure. They may also be 

 seen more or less well preserved in suitable sections. In the 

 closed ampulla of Pleuronectes sp., Hensen measured hairs 

 0.19-0.2 mm. The breadth of the ampulla over the crista was 

 0.5 mm. The actual length of the hairs was 0.4 mm. The 

 hairs after removal from the ampulla measured (maximum) 

 0.12 mm. 



Owing to thickness of the ampullar walls and pigment de- 

 posit the Frog's auditory hairs are invisible in the unopened 

 ampulla. They measure 0.12 mm. when taken out, and are 

 probably at least 0.2 mm. long in the uninjured state. Every 

 motion of the water throws these hairs into the greatest confu- 

 sion, tangling them in hopeless fashion ; and they remain as a 

 compact, gelatinous, spongy tissue or more solid mass. In this 



