STAR-FISH AND SEA-URCHINS. 295 



of that line, assume various movements and 

 shapes. The central portion is particularly apt to 

 take on the form of an arch, in which the central 

 end of the severed ray and the line of nerve-section 

 constitute the points of support (tetanus ?) (Fig. oQ), 

 or the central end may from the first show paralysis, 

 from which it never recovers. The distal end, on 

 the other hand, usually continues active, twisting 

 about in various directions, and eventually fasten- 

 ing its tip upon the floor of the tank to begin the 

 spiral movement of righting itself This movement 



Fi g. 56. Movements performed by a detached ray of a Star-fish, in which the 

 central nerve-trunk is divided. 



then continues as far as the line of nerve-injury, 

 where it invariably stops (Fig. oQ). The central 

 portion may then be dragged over into the normal 

 position, or may remain permanently inverted, 

 according to the strength of pull exerted by the 

 distal portion ; as a rule, it does not itself assist in 

 the righting movement, although its feet usually 

 continue protruded and mobile. Thus, the effect of 

 a transverse section of the nerve in a ray is that 

 of completely destroying physiological continuity 

 between the pedicels on either side of the section. 



