PLATE 5 



EXPLANATION OF FIGURES 



46 Second maturation spindle lying with its long axis parallel to a tangent 

 to the surface of the egg. Perivitelline space formed around egg cytoplasm. 

 First polar cell attached to fertilization membrane. (X 1700) 



47 Second maturation spindle rotated so that its long axis is perpendicular 

 to a tangent to the surface of the egg. Sperm nucleus beginning to break up 

 into chromosomes. Male centrosomes, surrounded by denser cytoplasm, at one 

 side of the sperm nucleus. (X 1700) 



48 Secondary oocyte showing early anaphase spindle, side view. Sperm 

 nucleus breaking up to form discrete chromosomes. (X 1700) 



49 Same spindle as figured in 48, showing longitudinal (reductional) division 

 of tetrad chromosomes. Centrosomes very indistinct. Spindle fibers not in 

 definite strands. (X 4050) 



50 Polar view of sister plates of the same anaphase spindle, showing dyad 

 nature of the eighteen daughter chromosomes. (X 4050) 



51 Late anaphase of second maturation spindle, side view. (X 1700) 



52 Formation of second polar cell. Chromosomes of male origin clearly 

 differentiated. Mitochondrial granules showing distinctly. (X 1700) 



53 Male and female pronuclei organized, each with eighteen dyad chromo- 

 somes. Centrosome couple of male origin with its surrounding aster well differ- 

 entiated. (X 1700) 



54 Male pronucleus with only twelve dyad chromosomes, the female with 

 eighteen. (X 1700) 



594 



