70 



Journal of Entomolog\ and Zoology 



to form a ring or pentagon of nervous tissue. From this ring 

 strands run out to each arm and branch and are distributed to the 

 arms, running embedded in the ossicles of the arms. 



Carpenter, '66, and Marshall, '84, found that the aboral nerv- 

 ous system controls the movements of the animals. If the cham- 

 bered organ is destroyed the animal is paralyzed, but it will swim 

 readily or make the necessary movements just as well when the 

 whole ambulacral nerve ring and alimentary canal are removed. 



Fig. 33. Nervous system of Crinoids. A. Diagram of a section through the 

 body of a crinoid showing nervous system by heavier lines. B. 

 Diagram of a section of the nervous system of a ci'inoid, nerves in 

 black, after Marshall. C, D, and E. Diagrams of the central nerv- 

 ous system of Crinoids, after Marshall and Carpenter. F. Dia- 

 gram of the plan of the nervous system of a crinoid. 



The commissural connectives between the aboral nerves co- 

 ordinate movements and if these are cut the arms move independ- 

 ently. 



The position of the radial cords within the bony plates comes 

 about gradually from larval conditions when they are open, 

 trough-like grooves. These grooves gradually close in. 



The cirri each have nerves from the central aboral nerve 

 mass. The arms, the cirri and the palps are tactile organs. 



Hamann has shown nerve endings in the surface epithelium 

 as well as by means of little projections with fine hairs at their 

 ends. 



Among the important contributions to the nervous system of 

 this group are those of Carpenter, 1865-84, Teuscher, '76, Ludwig, 

 '77, Hamann, '87, Cuenot, '91. The papers of Hamann, Carpenter, 

 Marshall and Haanen are among the most valuable contributions 

 to our knowledge of the nervous system. 



