FIG. 151. The maturation and impregnation of the animal ovum (diagrammatic). 

 A, the ovurn, surrounded by the vitelline membrane (ntem), in the act of forming 

 the first polar cell (pol) ; 9 cent, centrosome. B, both polar cells (pol) are formed, 

 the female pronucleus ( $ pron) 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 (<$ pron), its middle 

 piece the male centrosome ( o* cent) ; other structures as before. D, the male 

 and female pronuclei are in the act ot conjugation. E, conjugation is complete, 

 and the segmentation nucleus (seg. nucl) formed. (From Parker and HaswelTs 

 Zoology.) 



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