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 widely 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metallic rods, if carefully applied to them, may be withdrawn 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 
É Srg have 
