PKENTISS: THE OTOCYST OF DECAPOD CRUSTACEA. 219 



ratios to those of the volume of organ pipes, we should have, if the hairs 

 responded to different sound vibrations, an auditory organ with a rauge 

 of three octaves. 



To prove that his hypothesis was correct, sound waves were conducted, 

 by a mechanical contrivance modelled after the middle ear of mammals, 

 into the water of a vessel containing Mysis, the so-called auditory hairs 

 of which were under observation by the microscope. When notes of 

 a certain group were sounded on a musical instrument, a certain hair 

 would vibrate and disappear from view. Others would also respond, but 

 each to different sets of notes. 



Having proved that the different hairs responded to different sound 

 waves, Hensen next determined that Crustacea would react to vibratory 

 stimuli. A resonant bar of wood was floated in a vessel containing free- 

 swimming individuals of the genera Mysis and Palaemon. When the bar 

 was struck, both forms responded by a strong leap away from the source 

 of the sound. Palasmon reacted even more strongly when rendered 

 sensitive by gradual strychnine poisoning. 



Milne-Edwards ('76), Jourdain ('80), Delage ('87), and many others 

 have accepted the sense of audition in Crustacea as a fact. 



Garbini ('80, p. 192) uncritically remarks: "Che i crostacei odano 

 e indubitato ; lo sanno anche i pescatori, i quali devono avvicinarsi loro 

 in silenzio" (That Crustacea hear is undoubted ; this the fishermen know 

 well, who, when they capture them, approach in silence). 



Individuals of Paltemonetes varians, which he kept in an aquarium, 

 sprang backward at the slightest sound. 



Delage ('87) was the first to discover another function than that of 

 audition for the otocyst. By cutting off or destroying the sacs, he 

 proved that they functioned also as organs of orientation. Animals so 

 operated upon (Mysis, Palaemon, and Polybius among Crustacea) were 

 unable to keep their normal upright position in swimming. Blinding 

 intensified the effect, showing that sight aided in orientation. 



The otocyst may therefore, in his opinion, be compared to the sim- 

 plest form of the, vertebrate ear, — that found in Myxime, — where the 

 semicircular canals and utriculus serve the purpose of orientation, the 

 sacculus that of audition (to intensity of soimd). In the otocyst of 

 Crustacea both functions are performed, he believes, by the same 

 organ. 



Verworn ('91) proved that the otocyst of Ctenophores served simply 

 for oi-ientation, not being sensitive to sounds. 



Bunting ('93) confirms the conclusions of Delage as to the function 



