Plate VI. 



a: posterior ventral arms. 



b: anterior dorsal arms*). 



c: posterior dorsal arms. 



d: anterior ventral arms. 



e: ear-like lobes. ' 



f: the same. 



g: the same. * 



m: mouth. 



n : anus. 



œ: œsophagus. 



p : water-pore. 



r: intestine. 



St: stomach. 



w: the left vaso-peritoneal vesicle in the act of separating into enterocoel and hydrocoel. 



x: ectodermic invagination. 



y: point where the posterior dorsal arms begin to protrude. 

 Fig. 86. Pluteus at the beginning of the second developmental stage, about eight days old. Side 



view. 

 T> 87. Pluteus in a more advanced stage, about ten days old. Dorsal view. 

 B 88. Pluteus somewhat older than that in fig. 86. Side view. 

 B 89. Sketch of a Pluteus at the beginning of its second stage. Dorsal view. 

 » 90. A fully mature Pluteus about twenty days old or more. Seen from the ventral surface. 



Length including the arms: 1 mm. 

 Ï 91. Sketch of a Pluteus slightly older than that in fig. 89. Dorsal view. 



*) On pages 40 and 45 the reader will observe that the expression »anterior ventral arms» 

 has been used for »anterior dorsal arms» and vice versa. 



