STAR-FISH AND SEA-URCHINS. 297 
operation. When placed upon their dorsal surface, 
they turn up all their rays with a peculiar and 
exactly similar curve in each, which gives to the 
animal a somewhat tulip-like form (Fig. 58). This 
form is never assumed by unmutilated specimens, 
and in mutilated ones, although it may last for a 
long time, it is never permanent. In detached rays 
Fig. 57. Un-codrdinated movements of a Star-fish, in which the nerves of all the 
rays have been divided. 
this peculiar curve is also frequently exhibited ; but 
if the nerve of such a ray is divided at any point in 
its length, the curve is restricted to the distal 
portion of the ray, and it stops abruptly at the line 
of nerve-section. When entire Star-fish are mutilated 
by a section of each nerve-trunk half-way up each 
ray, and the animal is then placed upon its back, 
the tetanic contraction of the muscles in the rays 
