132 Darwin, and after Darwin. 
II. Tia. 
Fic. 38 —Formation and conjugation of the pronuclei in Ascaris megalocephala, 
(From Quazn's Anatomy, alter E. von Beneden.) 4 female pronucleus ; 7, 
male pronucleus; /, one of the polar bodies. 
I. The second polar body has just been 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. 
Ila. 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. 
IfI. Onty the female pronucleus is shown in this figure. The skein is contracted 
and thickened. The attraction-sphcres are near one side of the ovum, and are 
connected with its periphery by a cone of fibres forming a polar circle, p.c¢. ; 4.¢., 
equatorial circle. 
III 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. 
