64 



THE CRAYFISH 



[CH. II 



be placed to the right but below the animal, then OD 1 

 and OD are in the same direction and reinforce each 

 other, producing an increased pressure OD 2 upon the setae. 

 The sensation now caused is that of slipping down to 

 the left and the animal adjusts its body accordingly 

 (Fig. 12). Kreidl offers no explanation of the effect 



Fig. 12. 



of the pull-components OZ, OZ 1 . I have somewhat 

 modified the mechanical presentation of the argument as 

 expressed by the deviser of the experiments, but believe 

 that the main substance of the reasoning is identical. 



It would be interesting to try the effect of placing the 

 magnet vertically above the animal, a position apparently 

 not selected by Kreidl. If the magnet were of sufficient 

 strength to entirely neutralise the force of gravity and 

 draw the iron particles upward, one would expect the 

 animal to 'turn turtle' and remain inverted so long as 

 the magnetic force persisted. The terms ' statocyst ' and 

 ' statolith,' suggested by Kreidl in place of ' otocyst ' and 

 'otolith' respectively, are far preferable, and may with 



