WORMS. 315 



this are now drawn up close, and extend their bristles ; 

 these catch in like manner ; then an elongating move- 

 ment takes place ; the pencils of the anterior segments 

 being now retracted, they yield to the movement and 

 are pushed forward, while the others are held firm l)y 

 the resistance of their holding bristles ; thus gradually 

 the foreparts of the animal are exposed. 



But this gradual process would ill suit the necessity 

 of a creature so sensitive to alarm, when it wishes to 

 retreat. We have already seen how, with the fleetness 

 of a thought, its beautiful crown of scarlet plumes dis- 

 appears within its stony fastness : let us now look at 

 the apparatus which effects this movement. 



If you look again at this Serpula recently extracted, 

 you will find, with a lens, a pale yellow line running 

 along the upper surface of each foot, transversely to 

 the length of the body. This is the border of an ex- 

 cessively delicate membrane ; and on placing it under 

 a higher power (say 600 diameters), you will be aston- 

 ished at the elaborate provision here made for pre- 

 hension. This yellow line, which cannot be appreciated 

 by the unassisted eye, is a muscular ribbon over which 

 stand up edgewise a multitude of what I will call 

 combs, or rather sub-triangular plates. These have a 

 wide base ; and the apex of the triangle is curved over 

 into an abrupt hook, and then this is cut into a number 

 (from four to six) of sharp and long teeth. Tlie plates 

 stand side by side parallel to each other, along the 

 whole length of the ribbon, and there are muscular 

 fibres seen afiixed to the basal side of each plate, which 

 doubtless give it independent motion. I have counted 

 136 plates on one ribbon ; there are two ribbons on 

 each thoracic segment, and there are seven such scg- 



