S70 



PATTERNS AND PROBLEMS OF DEVELOPMENT 



by localized radiation, and pressure and centrifuging have been employed 

 in experimental analysis. The ovarian oocyte is more or less pear-shaped 

 and attached to the rhachis of the gonad by its slender end. Supposedly 



D E 



Fig. 179, A-E. — Early cleavages of Ascaris megalocephala. A, two-cell stage, spindles ot 

 second cleavages indicated; B, four-cell stage; C, the change in cell position to form the 

 "rhombus"; D, four-cell stage after change in position, the rhombus; E, seven cells, showing 

 asymmetry in position of the four dorsal cells. In the figures dorsal is above; anterior, right 

 (after Boveri, igioh). 



the blunt free end becomes the apical pole. Normally the egg becomes 

 spherical before polar-body formation; but in eggs which retained the 

 elongated form until fertilization and shell formation, polar bodies were 



