-55- ."' , 5i 



as might be expected from the configuration of the nervous system, that 

 the mechanism of the deviation reaction is altogether different from 

 the mechanism involved in a change of direction rhen the tips of the 

 rays are stimulated. In the one case we are dealing with the relatively 

 constant threshold of the receptors in the end of the ray while in the 

 other oase we are dealing with factors that vary with the mechanical 

 data of load and friction. 



In order that the obstacle may be left behind in the devia- 

 tion reaction there is usually a turn of at least 70 which is often 

 recovered from, by the operation of a tendency, whose mechanism I have 

 not worked out, to continue crawling in the saue direction as before 

 the disturbance, even if the action involve an actual change of direc- 

 tion, back, from one assumed as the result of the disturbance* This 

 tendency will also be noticed in connection with the righting reaction 

 (P. 75). 



COORDINATION OF MOV3lteNT8 OF THiS TUBfl F&ST WITH TKOSB OF 



THS ABM AS A WHO 18. 



Il.lus t ra t long o f the tendency of an arm to set itself more 

 ajt right angles tp_ its actively .en-ten teat tube feet, when such move- 

 ments involve dorsal and vent ral fleion and lateral twisting. 



If an active starfish be suspended and a solid object be 

 brou^it in contact with the tip of one of the rays, there will be a 

 movement of the tube feet in the direction 



