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. 56), 
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 
Fig. 56. Movements performed by a detached ray of a Star-fish, in which the 
; central nerve-trunk is divided. 
then continues as faras the line of nerve-injury, 
where it invariably stops (Fig. 56). 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. 
