306 EVENINGS AT THE MICEOSCOPE. 



Nature takes adroit advantage of mechanical principles 

 in the attainment of her ends." * 



Look now, in illustration of these principles, at the 

 bristle-feet of this beautiful green Phyllodoce. No 

 doubt you have often seen it in the little hollows of our 

 rocky ledges, and especially on beds of young mussels, 

 and probably you have admired the elegant ease with 

 which its lithe and tortuous body writhes and winds, 

 like a bit of green silken cord, in and out among the 

 compactly crowded shells. You have wondered, too, at 

 the difficulty which attends the attempt to take it up, 

 not on account of the rapidity of its motions, but be- 

 cause of the extreme slenderness and slipperiness of the 

 subject, and of the power which it possesses of insinu- 

 ating itself into the smallest crevice. 



The foot in this genus has but a single branch, and 

 a single pencil of bristles, which is placed between the 

 flat swimming leaf that ornaments each segment and 

 the lower oirrus. The bristles are of the compound 

 jointed form, but the joint is fixed in a peculiar manner. 

 The basal portion is drawn out into a very slender long 

 straight shaft, terminating in a knob somewhat resem- 

 bling the end of a limb-bone. This is slit in one direc- 

 tion to receive the terminal piece, which is shaped 

 somewhat like a lance-head, and is inserted into the slit 

 exactly as a knife-blade is fixed into the haft. The 

 head is in fact a knife-blade, with a thickened back and 

 a very thin edge, which is notched into teeth of the 

 most exquisite delicacy. The blade is slightly curved, 

 and drawn out into a long acute point ; and the whole 

 bristle is formed out of an elastic horny substance (prob- 



* Kep. on Brit. Annelidse, 211. 



