354 J. M. D. OLMSTED 



But the latter organ is concerned with two functions, hearing 

 and maintenance of equilibrium. Quatrefages ('42) could find 

 nothing like audition in Synapta inhaerens, and Semon ('87) re- 

 ported that the synaptids which he examined were 'tone-deaf.' 

 Nevertheless Semon thought it probable that the 'Baur'schen 

 Horblaschen,' or otocysts, were for the perception of other kinds 

 of vibrations, since the animals were very sensitive to shaking 

 (Erschutterungen) . Ludwig und Barthels ('91) agree with 

 Semon that the " Horblaschen auch an den erwachsenen Thieren 

 als Sinnesorgane functionieren," though they give no grounds for 

 their belief. 



Clark ('98) suggested that in Synapta vivipara (Synaptula hy- 

 driformis) the " otocysts do not function as hearing organs at all, 

 but are of use to indicate the animal's position." He describes 

 these organs as ten in number, " lying external to the radial 

 nerves at the point where they bend backwards over the cal- 

 careous ring." They are sacs 60 to 70 n in diameter, filled with 

 fluid in which floats or lies a 'cell' which may act as an otolith. 

 In a second paper Clark ('99) records important observations on 

 these organs in Synapta inhaerens and S. roseola, which he 

 studied in the living condition under the microscope. The 

 structure of the otocyst is the same in these species as in Synap- 

 tula hydriformis. The otolith changes its position when the 

 position of the otocyst is changed. The makeup of the organ 

 and the behavior of the enclosed otolith are in perfect accord 

 with the requirements of a 'positional organ,' i.e., a surface in 

 intimate connection with nerves on one side, and on the other 

 with a body which changes its relation to that surface whenever 

 the whole structure is moved. But the experiments which 

 Clark performed show merely that his synaptids were affected 

 by change of position. The conclusion that it was the "posi- 

 tional organs" which determined this behavior is an inference 

 only. 



Becher ('09) described similar 'Horblaschen' in Leptosynap- 

 tula bergensis, and found that they, too, meet the requirements 

 of a 'statocyst.' He also tried tones, and vibrations of lower 

 frequencies, but could observe no response. His statement 



