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 mul- 

 titude 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 



HOOKS OF SEBPULA. 



number of prehensile comb-like plates on this portion of 

 the body to be about one thousand nine hundred, each 



