Fig. 2.6. Adaptation of Extrovert of Arenicola marina to 

 Depression of Salinity 

 At beginning of experiment preparation was in normal sea water. First arrow indi- 

 cates start of progressive dilution; second arrow, termination of dilution two hours 

 later, when concentration had fallen to 28 % sea water. Second record shows accom- 

 modation to diluted medium, at low amplitude, six hours later. Time scale in minutes. 

 (From Wells and Ledingham (144).) 



20 r 



05 j.0 j -5 2 



A External Medium 

 Fig. 2.7. Osmotic Relations in Polychaetes 

 The curves show variation in concentration of internal with external medium. Nereis 

 diversicolor regulates at low concentrations; N. pelagica and Arenicola marina remain 

 isosmotic with the environment. (Based on data of Schlieper's, 1929.) 



