FTG. 17 

 Egjj; and larvae of the mollusk DeninJium. A is the egg just after fertilization, 

 showing a broad equatorial pigment zone and two white polar areas. B, normal 

 larva of 72 hours. C, active larva of the same age, from an egg from which the 

 lower polar area had been cut away, lacking the foot, shell and other important 

 structures. 



