HALF AN HOUR WITH SEA-WORMS. 73 



the creature has been placed in a marine aquarium 

 for some time, and got more or less used to the place. 

 Occasionally you may catch a glance at it spreading 

 out its brilliant scarlet plumes, but the moment your 

 shadow has fallen over the water, so sensitive is it, the 

 plumes are withdrawn, and the tube closed by a scarlet- 

 coloured plug, which when drawn down serves as the 

 stopper. These plumes are the branchiae the organs 

 of breathing. Every filament that gives to them 

 their feather-like and graceful appearance is finely and 

 abundantly ciliated. The surrounding water is dis- 

 turbed by their waving movement, and thus not only 

 furnishes them with fresh oxygen, but also brings 

 to them their food. The blood thus aerated is then 

 driven back to what serves as the heart by the con- 

 tractile power of the branchiae. As a rule, the sea- 

 worms which do not possess tubes have the gills or 

 branchiae arranged in tufts along each side of the 

 body, as in the lob-worm. But as the formation of a 

 tube for defensive purposes forbids this arrangement 

 in the serpula, we can at once see the beautiful arrange- 

 ment which collects and places them at the head of the 

 animal. The plug to which reference has just been 

 made is nothing more than one of these branchial 

 filaments modified and thickened. The movement 

 up and down the tube is achieved by means of bristle- 

 like attachments arranged along the sides. The 

 rapidity with which the serpula can withdraw itself 

 within its tube is strikingly in contrast with the 

 slowness and caution it exhibits before it again ex- 



