Puh. Puget Sound Biol. Sta. Vol. 2, No. 32 



PLATE 2 



z\ I., Ventral unpaired arm of the preoral lobe. 



d. I., Dorsal paired arms of the preoral lobe. 



/. d.. Fixing disk. 



s. d.. Sinistral disk. 



h. p. \,h. p. 2, h. p. 3, h. p. 4, h. p. 5, Hydrocoele pouches Nos. 1 to 5. 



Fig. 3. Egg with egg membrane for comparison of size with later 

 stages. X 'i4'- 



Fig. 4. Young larva with membrane removed to show the arms of 

 the preoral lobe just appearing; sinistral view. X "i^. 



Fig. 5. Slightly later stage than figure 4, showing growth of the pre- 

 oral lobe ; sinistral view. Membrane removed. X ~^^- 



Fig. 6. Typical symmetrical larva before any external evidence of 

 metamorphosis appears; sinistral view. Membrane ruptured before re- 

 moval. Preoral lobe distinct from the yolk-filled body of the larva. X i^- 



Fig. 7. Larva showing first signs of metamorphosis in the appear- 

 ance of the sinistral disk in oblique position on the left side of the larva. 

 X 44. 



Fig. 8. Larva in which the margins of the sinistral disk betray the 

 appearance of the first 5 hydrocoele pouches. X 44. 



