EMBRYOLOGY OF ECHINODEEMS. 



137 



On the outer surface of the corresponding portion of 

 the opposite, or right water-tul^e, and therefore on the 

 opposite side of the stomach, calcareous spicules make 

 their appearance, and build up a spiral band (oi), which 



€L 



Fig. 81. 

 Fig. 81. — Side view of the same lana. (Drawn from nature by E. B. 

 Wilson.) 



am^, arn^, am^, am*, aniK The five water tubes of starfish. 

 Other letters as in Fig. 80. 



