274 EVENINGS AT THE MICROSCOPE. 



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 exceedingly delicate 

 membrane ; and on placing it under a higher power (say 

 600 diameters) you will be astonished at the elaborate 

 provision here made for prehension. This yellow line, 

 which cannot be perceived 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. The 

 plates stand side by side, parallel to each other, along the 

 whole length of the ribbon, and there are muscular fibres 

 seen affixed 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 segments ; — hence we 

 may compute the total number of , prehensile comb-like 



HOOKS OF SERPULA. 



plates on this portion of the body to be about one thousand 

 nine hundred, each of which is wielded by muscles at the 



