BEARERS OF THE HEREDITARY QUALITIES (ii. 



Fig. 15. — Diagram of the process of fertilisation in Ascavis. (After Boveri.) 



a, female pronucleus ; 6, polar bodies ; c, sperm pronucleus ; d, sperm-cap ; ac, chromosomes 

 of united female and male pronuclei (a and c) ; e, centrosomes ; fine (archoplasmic) threads 

 radiating from the centrosomes. I-V show union of paternal and maternal chromosomes ; 

 VI shows equatorial plate of segmentation nucleus ; VII-X show the division into the two 

 first cleavage-cells or blastomeres. 



