ORIGIN OF THE INDIVIDUAL 



255 



G 



Fia. 132. Development of a Mollusc (Dentalium) , after removal of the 'polar 

 lobe'. A, egg, shortly after being extruded and before maturation is completed, show- 

 ing three differentiated regions. B, section through an egg after fertilization, showing 

 cytoplasmic rearrangement involving the segregation of clear ' polar lobe ' at p. C, nor- 

 mal eight cell stage with 'polar lobe' in cell D; D, normal sixteen cell stage, with materi- 

 als of polar lobe now in cell X; E, sixteen cell stage, from an egg with the 'polar lobe' 

 removed at the first division; F, normal larva at end of twenty-four hours; G, larva 

 (abnormal) of same age developed from egg from which 'polar lobe' was removed; 

 H, normal larva of seventy-two hours. /, abnormal larva of same age from'lobeless* 

 egg. (From Kellicott, after Wilson.) 



