ECHINODERMATA 163 



in the five ambulacral grooves on the ventral sides of the 

 arms. The mouth is the circular opening in the center 

 of the ventral surface. 



To study the internal organs place the specimen in a 

 pan of water deep enough to cover it, and with the scissors 



FIG. 188. Ventral or under surface of the starfish. Black circle in the middle 

 is the mouth from which radiate the five ambulacral grooves, each filled with 

 about a hundred feet. Photograph half natural size. 



remove the skin from nearly half the dorsal surface cutting 

 alongside the madreporic plate remaining in place. The 

 saclike stomach occupies the body just beneath the skin 

 and from it bifurcated processes, the pyloric cceca, extend 

 more than half way to the ends of the arms. By slightly 

 raising the skin bearing the madreporic plate, the slender 

 stone canal may be seen leading to the ring around the 



