Plate XXIV 



Development of Dentalium, from WILSON (1904). 



a. Egg before development with upper and lower clear zones. 



b. Formation of the yolk-lobe at the lower pole. 



c. First segmentation division ; the yolk-lobe is not divided. 



d. Normal larva with anterior tuft of cilia and post-trochal cone. 



e. Larva derived from an egg from which the yolk-lobe was cut off. 



