474 



F. W. GAMBLE AND J. H. ASHWORTH. 



Table showing the dimensions of the Brain and Ventral 

 Nerve-cord at different stages of growth of the species 

 of Arenicola. Measurements in millimetres. 



This table shows that the linear dimensions of the brain in- 

 crease in the same proportion as does the length of the body 

 from the post- larva to a stage when the body measures about 

 17 mm. Beyond this limit the brain increases more slowly, 

 and attains its maximum ('9 to 1 mm. in length) in specimens 

 120 to 250 mm. long, according as they belong to the littoral 

 or Lamiuarian varieties of the lugworm. 



