138 ANIMAL LIFE AND SOCIAL GROWTH 



its life on the proboscis but lives on the yolk that 

 has been stored in the egg. In the later stages 

 of its life it has the parasitic habit. There is good 

 evidence that the developing male receives some 

 material from the proboscis of the female which 

 starts it going in the male direction. The female 

 does not need to be mature in order to exert this 

 influence and even the female proboscis alone or 

 extracts of it will have the same effect. 



If the young, neuter larvae do not come into 

 contact with a female, they remain indifferent 

 for some ten to twelve days and then begin trans- 

 formation in the female direction. This peculiar 

 lability of sex in Bonellia has survival value for the 

 species. The worm is not abundant even in the 

 Bay of Naples, where it occurs in numbers in but a 

 few places. If the sexes were unalterably deter- 

 mined at hatching in the usual 50-50 sex ratio, 

 then the males must needs find a female before 

 they could function and there would be consider- 

 ably greater loss from isolation than now occurs. 

 When the larvae first hatch, they are positive 

 to light and swim away from the egg mass. 

 There is evidence that they do not attach to their 

 own mother although they may attach immedi- 

 ately to a neighboring female. If they fail to find 

 a female during this free swimming stage, the 

 chances of which are greater than if there were 



