worms. 275 



of which is wielded by muscles at the will of the animal ; 

 while, as each plate carries on an average five teeth, 

 there are nearly ten thousand teeth hooked into the 

 lining membrane of the cell, when the animal chooses 

 to descend. Even this, however, is very far short of the 

 total number, because long ribbons of hooks of a similar 

 structure, but of smaller dimensions, run across the 

 abdominal segments, which are much more numerous 

 than the thoracic. No wonder, with so many muscles 

 wielding so many grappling hooks, that the retreat is so 

 rapidly effected ! 



t 2 



