■ A. R. MOORE 321 



movements; (c) the longitudinal interskeletal dorsoflexors of the ray 

 floor; (d) the longitudinal interskeletal ventroflexors of the ray 

 floor. 



It will be shown elsewhere that limited parts of each system are 

 independently innervated and are capable of independent action. 

 This permits the ray to bend either dorsally or ventrally at any 

 point, and to twist the peripheral part on its long axis through any 

 angle up to 180°. 



Motor Nerve Elements. 



It has been found that strychnine^ and nicotine are without excita- 

 tory action on the neuromuscular system of the ccelenterate Metri- 

 dium. It may be assumed then that the alkaloids in question, in 

 the case of echinoderms and the higher forms, act on elements of the 

 neurone especially developed in the more complex types of nervous 

 system. The contraction of certain groups of muscles as the result of 

 the action of nicotine or of strychnine consequently becomes an indi- 

 cator of chemical excitation of the corresponding nervous elements. 

 If we assume that the excitatory action of nicotine and strychnine is 

 on some part of the motor neurone such as the sensory-motor junc- 

 tion, it would then follow as to the loci of the action of the alkaloids 

 that (a) both substances excite the motor neurones of the dorsal 

 sheath; (b) both sustances excite the motor neurones innervating 

 the muscles of the ray floor which cause ventral flexure; (c) strych- 

 nine excites the motor neurones governing the dorsoflex musculature 

 of the ray floor; they are refractory to nicotine. 



Sensory Nerve Elements. 



Ordinarily when an Asterias is laid on its back on the floor of an 

 aquarium the rays begin their dorsal bending quite promptly, and 

 righting is accomplished in 1 or 2 minutes. If, however, the aquarium 

 jar has a cone-shaped floor and the inverted animal is placed so that 

 its central disk rests on the apex of the cone, the righting is much de- 

 layed, since in this case the rays only by chance come into contact 



5 Moore, A. R., Proc. Nat. Acad. Sc, 1917, iii, 598. 



