Structure and Economy of Spiders. 473 



straight and exceedingly attenuated ; and upon each of them is 

 disposed a tortuous white line inflected into short curves and 

 loops like a ravelled thread of fine silk. A pale blue band, 

 thickly distributed on each of the inflected lines in numerous 

 irregular curvatures, completes the flocculus. The flexures of 

 the pale blue bands are more vpidely extended than those of 

 the white tortuous lines on which they occur, and to them the 

 adhesive property of the snare is chiefly to be ascribed, in 

 attempting to determine by experiment the cause of adhesion 

 in the blue bands, I ascertained that bodies with highly polished 

 surfaces, such as the bulbs of thermometers and burnished 

 metallic rods, if carefully applied to thera, may be withdrawn 

 without deranging their structure, though the viscid globules 

 in the nets of Geometric Spiders adhere to the same bodies 

 as soon as they are brought into contact with them. From this 

 circumstance I was led to infer that the blue bands are fibrous, 

 although their structure is so exceedingly fine that I cannot 

 detect it even with the assistance of the microscope ; and that 

 the imperceptible filaments of which they are composed adhere 

 to objects, not in consequence of being glutinous, but solely by 

 attaching themselves to inequalities on their surfaces. The 

 following brief description of the manner in which the flocculi 

 are fabricated, and of the curious apparatus employed in the 

 process, gives additional weight to this opinion. 



There are on the upper joint of the tarsi of the posterior legs 

 of Clubiona atrox two parallel rows of spines, moveable at the 

 pleasure of the animal, which may readily be discerned by 

 means of a lens having a magnifying power of ten or twelve. 

 They are situated upon a prominent ridge on the abdominal 

 side of the superior region of the joint, commencing just below 

 its articulation with the tibia, and terminating in a strong spur 

 near its lower extremity. The spines composing the upper row 



3 p 2 have 



