220 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



of the otocyst iu geotropic orientation. When the otocysts of young 

 crayfish were destroyed, especially if their chelae were also removed to 

 render their position in the water less stable, there was the same loss of 

 power of orientation that had been observed by Delage. 



Kreidl ('93), in order to avoid the disturbance to the normal condition 

 caused by the removal of the otocysts, made use of the following in- 

 genious experiment : Palaemonetes newly moulted, and thus without 

 otoliths, were placed in filtered water to which iron filings were added. 

 The otocysts were soon filled with the metallic particles, the chelae being 

 used to convey them to the opening of the ear in the dorsal wall of the 

 autennule. When now a strong electromagnet was held at one side of, 

 and slightly above the sacs containing the iron otoliths, the shrimp 

 would lean a little to one side, its dorso-ventral axis, normally coincident 

 with the direction of gravity, pointing away from the magnet. This new 

 position of the dorso-ventral axis is proved by mechanics to be the 

 resultant of the two pulls, that of gravity and that of the magnet, the 

 animal accommodating itself to the direction of the resultant of the two 

 forces. If the magnet were held to the right of the animal, the otocysts 

 would be stimulated in precisely the same way as by gravity alone when 

 the shrimp's dorso-ventral axis is artificially turned toward the right ; 

 the result is that it attempts to recover its normal position with reference 

 to gravity, and thus turns its vertical axis away from the magnet. Kreidl, 

 going a step further than his predecessors, affirms that the otocysts are 

 not auditory, but exclusively static in function. Thus they should be 

 called stato-cjsts, not o^o-cysts. 



Still further evidence as to their static function is supplied by Clark 

 ('96). The compensation movements of the eyestalks of the fiddler 

 crab (Gelasimus pugilator) and the lady crab (Platyonichus ocellatus) 

 were observed. Tilting a normal animal about its autero-posterior axis 

 gave a parallel compensating movement of the eyes through an angle 

 of 35° to 45°, whether the tilting was to the right or left. On rotation 

 about the dorso-ventral axis, no such movements are shown, thougli 

 •when rotated about the lateral axis, the animal's eyes moved in the 

 opposite direction through an angle of 35°. 



If both otocysts were removed, these compensative movements were 

 much reduced, and the general movements of the crab also became 

 very uncertain. 



After removal of one otocyst 94 per cent of the animals showed on 

 rotation toward the uninjured side less compensation than uninjured 

 animals. Blinding produced only a slight reduction in the compensatory 



