ANATOMY OF A STARFISH PEDICELLARIAE 



433 



The last-named ossicle increases the certainty of the grip by 

 fixing the lower parts of each blade in the same vertical plane, 

 and preventing lateral slipping, so that it serves the same pur- 

 pose as the pivot in a pair of scissors. Each blade, in fact, fits 

 into a groove on the side of this piece. 



The muscles which close 



Fig. 185. Asterias rubens, seen from the aboral surface, x 1. mad, Madreporite. 



the blades arise from the lower ends (handles) of the blades, 

 and are united below to form a common muscular string which 

 attaches the whole organ to one of the plates of the skeleton. 

 An attempt of the victim to tear the pedicellaria out is resisted 

 by the contraction of this string, which thus brings about a 

 closer grip of the blades. In order that the blades may open 

 they must first be lifted out of the grooves on the basal piece 

 this is effected by special lifting muscles. The opening is 

 vol. i 2 F 



