THE CRAYFISH 



263 



statocysts, a magnet was brought near it, and by moving 

 the magnet the particles of iron were caused to move as 

 they would be by a change in the position of the animal. 

 By this means the prawn was made to alter its position in 



B 



-grn. 



Fig. 167. — The statocyst of the crayfish. 



A , The right antennule, seen from the median side with the basal joint opened and 

 the ftagella cut short ; B t basal joint of the left antennule from above ; C, two 

 hairs from the statocyst. — C partly after Howes. 



en., Inner nagellum ; ex., outer flagellum ; grn., sand grains ; «., nerve of the 

 statocyst ; n.f., nerve fibres ; o., opening of the statocyst ; sic, statocyst. 



correspondence with the movements of the magnet. It was 

 formerly supposed that the statocysts subserved the sense 

 of hearing, but though the animals appear to perceive vibra- 

 tions, and this may be due to the statocysts, it is doubtful 

 whether the latter are true organs of hearing. We have seen 



