164 



ANARTHROPODA 



FIG. 189. Vertical section of one arm of a starfish ; a, anus ; 6, ampulla ; c, car- 

 diac stomach ; ct, connection of pyloric caeca with stomach ; d, stone canal ; i, 

 radial ambulacral vessel ; ft, feet ; m, mouth ; n, cut end of nerve ring sur- 

 rounding the mouth ; py, pyloric caeca ; r, respiratory organ ; rp, ovary ; st, 

 madreporic plate ; stc t stomach. 



mouth. The removal of the pyloric caeca makes visible 

 along the floor of the arm two rows of little bladders, 



FlG. IW. Strongylocentrotus: the green urchin on the left, and Arbacia the black 

 urchin on the right. The green urchin seen from the ventral side shows white 

 teeth filling the mouth and numerous feet among the spines. Photograph half 

 natural size. 



ampullce, which are usually in a collapsed condition. These 

 receive the water from the radial ambulacral vessel extend- 



