STAR-FISH AND SEA-URCHINS. 



297 



operation. When placed upon their dorsal surface, 

 they turn up ail their rays with a peculiar and 

 exactly similar curve in each, which gives to the 

 animal a somewhat tulip-lilvc 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. 5/ 



Un-coordinated movcm':>nts of a vStar-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 contractiju of the muscles in the rays 



