20 



SEX AND HEREDITY 



standing the difference of size and cleavage, the anther- 

 idium and the oogonium have features in common, which 

 point to their having originated in Descent from a common 



FIG. 10. 



Gametes and fertilization in Fucus. i, group of antheridia, borne on a 

 branched hair ; 2, part of an antheridium showing development of sperma- 

 tozoids ; 3, spermatozoid : a=eye-spot, =nucleus; 4, isolated antheridia 

 liberating the spermatozoids ; 5, egg surrounded by spermatozoids ; 6, section 

 through a fertilized egg; s&=nucleus of egg, spk = sperm-nucleus, sp= sperma- 

 tozoids. (i, 4, 5, after Thuret ; 2, 3, after Guignard ; 6, after Farmer. From 

 Strasburger's Textbook.) 



source. The spermatozoids are of the form usual for the 

 gametes of the Brown Seaweeds (Fig. 10 (3) ) . If sea- 

 water containing active spermatozoids be added to water 

 containing living ova, the latter attract the former, which, 



