Embryology. 



125 



in a singularly forcible manner. On this account, 

 therefore, and also because the facts will again have 

 to be considered in another connexion when we come 

 to deal with Weismann's theory of heredity, I will 

 here briefly describe the processes in question. 



We have already seen that the young egg-cell mul- 

 tiplies itself by simple binary division, after the 

 manner of unicellular organisms in general thereby 



FIG. 33. Stages in the formation of the polar bodies in the ovum of a 

 star-fish. (After Hertwig.) g.v., germinal vesicle transformed into a 

 spindle-shaped system of fibres ; p.', the first polar body becoming ex- 

 truded ; /., /., both polar bodies fully extruded ; fpn., female pro- 

 nucleus, or residue of the germinal vesicle. 



indicating, as also by its amoebiform movements, its 

 fundamental identity with such organisms in kind. 

 But, as we have likewise seen, when the ovum ceases 

 to resemble these organisms, by taking on its higher 

 degree of functional capacity, it is no longer able to 

 multiply itself in this manner. On the contrary, its 

 cell-divisions are now of an endogenous character, 



