ITS STOPPER. 173 



Take your pocket-lens now, and examine tlie struc- 

 ture of these brilliant organs in detail. Presto ! on 

 the slightest movement of your hand towards him, he 

 is gone ! He has retreated like a lightning flash into 

 his tube. But did you notice how cleverly, as he went, 

 he shut the door after him? A most marvellous 

 contrivance is here. Watch it as it again carefully 

 protrudes. There is a solid organ exactly conical, 

 seated at the end of a long flexible stem, which forms 

 the stopper : it is one of a pair of tentacles ; but as 

 only one could be of any service as a stopper, one 

 only is developed ; the other being minute. This 

 stopper is very beautiful ; it is always richly coloured, 

 usually orange, or vermilion, sometimes varied with 

 pure white : its flat extremity or top is made up of 

 ridges, which run from the centre to the circumference, 

 where they project in tiny teeth of the most exact 

 regularity. The fan-like expansions are formed of 

 radiating filaments, also very brilliant in hue, which 

 are the breathing organs, separating oxygen from the 

 currents of water which play along their ciliated 

 surfaces. 



There is no distinct head in these animals, but the 

 organs I have described are protected by a sort of 

 projecting mantle or hood, beneath which is the orifice 

 of the stomach. Eyes it seems to have, and most 

 sharp ones ; for, as we saw, the animal is peculiarly 

 sensitive to the approach of any object, even though 

 this be on the outside of a glass tank, at the bottom 

 of whose interior it is expanded. Yet I have searched 

 in vain for any distinct organs of vision. 



The mechanism by which the Serpula projects its 



