Plate XXIII. 



{Top left) The 'mitraria' larva of the worm Oweiiia fusiforiiiis. 



{Top right) The 'actinotrocha' larva o( Phorotiis. 



(Bottom left) The 'tornaria' larva of Bahvioglossus. 



{Bottom right) A pilchard egg from the plankton. 



Photographs by D. P. Wilson 



