176 ITS HOOKS. 



there are two ribbons on eacli thoracic segment, and 

 there are seven such segments: — hence we may 

 compute the total number of prehensile comb-like 

 plates to be about one thousand nine hundred, each 

 of which is wielded by muscles at the will of the 

 animal ; while, as each plate carries seven teeth, 

 there are between thirteen and fourteen thousand 

 teeth hooked into the lining membrane of the cell, 

 when the animal chooses to descend. No wonder, 

 with so many muscles wielding so many grappling 

 hooks, that the retreat is so rapidly effected ! 



A group of SerpulcB of the species which I have 

 been describing, is represented in Plate Y. 



