220 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
of the otocyst in geotropic orientation. When the otocysts of young 
crayfish were destroyed, especially if their chele 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: Palemonetes 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 chele being 
used to convey them to the opening of the ear in the dorsal wall of the 
antennule. 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-cysts, not oto-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 antero-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-ventra]l axis, no such movements are shown, though 
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 
