312 



EVENINGS AT THE MICROSCOPE 



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. 1 have counted 136 

 plates on one ribbon; there are two ribbons on each tho- 

 racic segment, and there are seven such segments hence 



HOOKS OF SBRPULA. 



we may compute the total number of prehensile comb-like 

 plates on this portion of the body to be about one thou- 

 sand nine hundred, each 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! 



