AND STAK-FISH. 165 



egg-urchin (Echinus sphasra), these spicules are 

 C-shaped, as shown in Fig. 88. The spicules of 

 another species of sea-urchin found on our northern 

 coasts (Echinus drobrachiensis) are very peculiar, 

 having the appearance of bent thigh-bones (Fig. 89). 



Fig. 88. Fig. 89. 



Spicules of Echinus sphxra. Spicules of Echinus drobrachiensis. 



The nervous system in the sea-urchins consists of 

 a ring which encircles the gullet, and thence sends 

 forth radiating branches to the various parts of the 

 body. The intestine is twisted or convoluted. The 

 interior of the shell and various parts is richly 

 lined with cilia, which keep up a constant circulation, 

 and distribute the fluids all over the body. Their 

 higher organization is further shown by the fact that 

 the sexes are separate, each possessing distinct 

 reproductive organs. The young, both of the sea- 

 urchins and the star-fish, do not resemble their 

 parents in the slightest degree. Indeed, the fry of 

 the former were esteemed a distinct genus of marine 

 animals, and named Pluteus. Whilst the adults 

 have a uniformly radiate, or star- shaped, structure, 



