132 Darwin, and after Darwin. 



11 a. 



FlG. 38. Formation and conjugation of the pronuclei in Ascaris megalocephala. 

 (From Quoin's Anatomy, after E. von Beneden.) f^ female pronucleus ; m, 

 male pronucleus ; J>, one of the polar bodies. 



I. The second polar lx>dy has just lieen extruded ; both male and female pronuclei 

 contain two chromatin particles ; those of the male pronucleus are becoming 

 transformed into a skein. 



II. The chromatin in both pronuclei now forms into a skein. 



II a. The skeins are more distinct. Two attraction (or protoplasmic) spheres, each 

 with a central particle united with a small spindle of achromatic fibres, have made 

 their appearance in the general substance of the egg close to the mutually 

 approaching pronuclei. The male pronucleus has the remains of the body of the 

 spermatozoon adhering to it. 



III. On'v the female pronucleus is shown in this figure. The skein is contracted 



ened. The attraction-spheres 



ide of the ovum, and are 

 of fibres forming a polar circle, f.c. ; e.c., 



nd thicke 



connected with its periphery by a 

 equatorial circle. 



Ill a. The pronuclei have come into contact, and the spindle-system is now 

 arranged across their common axis. 



IV. Contraction of the skein, and formation of two U- or V-shaped chromatin 

 fibres in each pronucleus. 



V. The V-shaped chromatin filaments are now quite distinct : the male and female 

 pronuclei are in close contact. 



