T.b.l. 



. hi. S.I. 



r.S. 



FIG. 31. SUCCESSIVE STAGES IN THE MATURATION, FERTILIZATION AND SEGMENTA- 

 TION OF THE STARFISH (ASTERIAS FORBESII) EGG. 



a, first maturation spindle (m.s.l) and the spermatozoon (s); 6, formation of the 

 first polar body (p.b.l) and the residual substance of the nucleus (r.s.); c, second 

 maturation spindle (m.s.2) ; d, female pronucleus ( 2 ) ; e, union of male ( $ ) and female 

 pronuclei (the male pronucleus is derived from the spermatozoon) ; /, first segmenta- 

 tion spindle; g, two-cell stage of division, d and e are less highly magnified. 



26 



