54 Ji(iirii:il lit Entomology ;ind ZiK)lo^y 



The pedicellariae of sea-urchins refuse to seize or hold each 

 other or parts of the bodies or others of the same species. Von 

 Uexkull believes this is due to a presence of a substance "auto- 

 dermin" which is in the skin. In sea-urchin pericellariae have the 

 power of indei)endent reactions. Each when isolated on a piece of 

 shell may behave as when on the body of the animal. The stimulus 

 from the pedicellariae need not pass through the radial nerves for 

 if the nerve is cut the reactions are as before. 



Ophiuroidea 



The nervous system of serpent-stars is more complicated than 

 that of starfish. The radial and circum-oral nerves are shut off 

 from the surface of the body and inclosed in a small cavity. The 

 more superficial radial and circum-oral nerves are well developed 

 and from the radial nerves fibers run out to the spines of the legs 

 and the tube-feet. These last are provided with ganglia at their 

 bases and with nerve strands running their length. The nerves 

 which run to the spines also have ganglionic thickenings upon 

 them at the bases of the spines. From the ganglia at the bases of 

 the tube-feet delicate strands run out to one epineural ganglion 

 for each tube-foot. On the ventral side of the disc on each side of 

 radial nerves lateral nerves run out to near the margin of the disc 

 communicating with the radial nerves and also connected with the 

 superficial nerve jjlexus on the lower side of the disc. There are 

 then in this way two lateral nerves from each arm base, and each 

 one of these sends out an inter-radial nerve. Nerves from the 

 circum-oral ring run to the teeth, five pairs in all. 



The deeper radial and circum-oral nerves are closely applied 

 to the more superficial nerves and appear much like parts of them, 

 being represented by groups of dorsally placed cells. These deeper 

 nerves are two for each arm. The circum-oral ring about the 

 mouth sends out pairs of nerves to the muscles of the arm. 



A system of so-called genital nerves is found quite distinct 

 and independent from the other systems. More or less isolated 

 loops of fibers are found in each area of the disc between the arms. 



Ilamann, 1888. gives one of the best accounts of the nervous 

 system. Delage and Herouard also figure and describe the nerv- 

 ous system in this group. The first author describes and figures 

 nerves coming out laterally from the chief radial nerve to be 

 applied to the skin. These may be the cutaneous nerves of Delage 

 and Herouard. 



Ilamann al.so shows strands from these to the tube-feet where 

 ganglia are located and from these ganglia are nerves with ganglia 

 running in to the center of the arm, and also nerves arching up 

 dorsally to end in small ganglia. These are very much in the posi- 

 tion as shown in the diagrams and figures. 



