Plate IX 



t 





* -s 



Four stages in the production of polar bodies in the egg of the Mollusc Physa 



fontinalis. From KOSTANECKI and WIERZEJSKI. 



Anaphase of first polar mitosis ; on the right, sperm head with aster appearing in 

 front of it. 



b. Telophase of first polar mitosis ; polar body being extruded 

 of spermatozoon. 



c. Metaphase of second polar mitosis ; first polar body completely extruded 

 sperm aster with divided centrosome widely separated from sperm head. 



</. Telophase of second polar mitosis, and extrusion of second polar body. 

 All the figures are reconstructed from more than one section. 



Below, head and tail 

 Below, 



