f>ol 



ycent 



2 pro ft 



FIG. 150. The maturation and impregnation of the animal ovum (diagrammatic). 



A, the ovum, surrounded by the vitelline membrane (inem\ in the act of forming 

 the first polar cell (Pol); 9 cent, centrosome. B, both polar cells (/W) are 

 formed, the female pronucleus (9 /TWZ.) lies near the centre of the ovum, and 

 one of the several sperms is shown making its way into the ovum at the micropyle 

 (microp). C, the head of the sperm has become the male pronucleus (6 pron), 

 its middle piece the male centrosome (<J cent) : other structures as before. 

 D, the male and female pronuclei are in the act of conjugation. E, conjugation 

 is complete, and the segmentation nucleus (seg. nucl) formed. (From Parker 

 and Haswell's Zoology.) 



