280 



SYSTEMATIC ZOOLOGY. 



CLASS IV. -ECHINOIDEA (SEA-URCHINS). 



In the sea-urchins the body is spherical, heart-shaped, or 

 disc-like, and the ambulacral areas extend, like meridians, 



FIG. 94. Crinoid (Pentacrinut}, half 

 natural size. From Brehm. 



FIG. 95. Mouth area of a crinoid 

 (Comatula), showing the course of 

 the intestine leading from the 

 mouth (m) to the vent (a), g, 

 grooves leading from arms to mouth. 



from oral to anal regions. In short, sea-urchins are easiest 

 compared with starfishes, if we imagine the arms of the 



