58 



SEX 



marine worm called Bonellia is a pigmy 

 parasite on its mate (see Fig. 11). 



Fio. 11. The peculiar green worm Bonellia viridis the 

 female (F) with a long retractile bifid grooved proboscis 

 (PR), and the pigmy male (M). (After Lacaze-Duthiers.) 



Fourthly, the dimorphism may find ex- 

 pression not in any peculiar structures or 



