i6 



SEX AND HEREDITY 



may be regarded as functionally female, and they act as 

 centres of attraction to gametes from other sporangia, 

 which gather round them in crowds, coming into contact 

 with them by their advanced cilia (Fig. 7 (i)). These 

 gametes which retain their motility may be held to be 



FIG. 7. 



Ectocarpus siliculosus. i, female gamete surrounded by a number of male 

 gametes, seen from the side ; 2-5, stages in the fusion of gametes ; 6, zygote 

 after 24 hours ; 7-9, fusion of the nuclei in conjugation, as seen after fixing and 

 staining. (1-5 after Berthold ; 6-9 after Oltmanns. FromStrasburger.) 



male. Finally, the cilium of one of them gradually 

 shortens and grows thicker, the male gamete approaching 

 the female till fusion of the two is fully carried out (Fig. 

 7 (2, 3, 4, 5) ) . The nuclei, which at first remained separate 

 (Fig. 7 (7, 8)), also fuse together (9), and the zygote is 

 then uni-nucleate. After the fusion begins all the other 

 gametes move away, the attraction having ceased. The 



