ITS ARRAY OF HOOKS. 175 



catch in like manner ; then an elongating movement 

 takes place ; the pencils of the anterior segm^ents heing 

 now retracted, thej yield to the movement and are 

 pushed forward, while the others are held firm by the 

 resistance of their holding bristles ; thus gradually 

 the foreparts of the animal are exposed. 



But the gi'adual 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 

 disappears within a stony fastness ; let us now look 

 at the apparatus which effects this movement. 



If we look at a Serpula recently dead, — which we 

 may readily do, since it is the habit of most tubicolous 

 Annelida to come out to die, — we shall 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 excessively delicate membrane, 

 and on placing it under a high power (say 300 dia- 

 meters) we are astonished at the elaborate provision 

 here made for prehension. This yellow line, which 

 cannot be appreciated by the unassisted eye, is a 

 muscular ribbon, on which stand up edgewise a mul- 

 titude of what I will call combs, or rather sub-trian- 

 gular plates. The edge of each plate is cut very 

 regularly into six teeth, which curve in one direction, 

 and one other curved so as to face these. The combs 

 stand side by side parallel to each other, along the 

 whole length of the ribbon, and there are muscular 

 fibres seen affixed to the smaller end of every plate, 

 which doubtless give it independent motion. I counted 

 one hundred and thirty-six plates on one ribbon ; 



