EMBRYOLOGY OF ECHINODERMS. 



137 



On the outer surface of the corresponding portion of 

 the opposite, or right water-tube, and therefore on the 

 opposite side of the stomach, calcareous spicules make 

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



a. 



FIG. 81. 



FIG. 81. Side view of the same larva. (Drawn from nature by E. B. 

 Wilson.) 



am 1 , am 2 , am 8 , am*, am 5 . The five water tubes of starfish. 

 Other letters as in Fig. 80. 



