STRUCTURE, FUNCTIONS AND CECONOMY OP ARANEIDEA. 63 



Some of the spiders belonging to the families TJieridiidcB and Epiiiridce 

 have the sides and lower part of the tarsi, at their extremity, supplied with 

 several small, curved, dentated claws, in addition to the three larger ones 

 common to them all. Epeira quadrata, Epeira apoclisa, and, indeed, most 

 of the larger species of EpeircB indigenous to Great Britain, exhibit this 

 structure to advantage under the microscope ; they have, besides, a strong, 

 moveable spine, inserted near the termination of the tarsus of each posterior 

 leg, on the under side, which curves a little upwards at its extremity, and 

 presents a slight irregularity of outline at its superior surface. These spines, 

 which have been denominated sustentacula, subserve an important purpose. 

 By the contraction of their flexor muscles they are drawn towards the foot, 

 and are thus brought into direct opposition to the claws, by which means the 

 animals are enabled to hold with a firm grasp such lines as they have occasion 

 to draw from the spinners with the feet of the hind-legs, and such also as 

 they design to attach themselves to*. 



There are on the superior part of the metatarsus of the posterior legs of all 

 the Cini/lo7iidce two parallel rows of moveable spines commencing just below 

 its articulation with the tibia and terminating near its lower extremity. In 

 a state of repose, the spines composing both rows are directed down the joint 

 and are somewhat inclined towards each other ; those of the upper row have 

 a considerable degree of curvature and taper gradually to a fine point, those 

 of the lower row being stronger, more closely set, and less curved. Employed 

 to transform, by the process of curling, certain lines proceeding from the 

 spinners into the small flocculi characteristic of the snares of the Cini/lonidce, 

 the double series of spines has received the name oi calamistrum. 



When a spider of this family purposes to form a flocculus, it presses its 

 spinners against one of the glossy lines constituting the foundation of its snare, 

 and, emitting from them a small quantity of liquid gum, attaches to it several 

 slender filaments, drawn out by advancing the abdomen a little, and kept 

 distinct by extending the spinning mammulas laterally. The posterior legs 

 are then raised above the plane of position, and the tarsal claws of one of 

 them are applied to the superior surface of the metatarsus of the other, near 

 its articulation with the tarsus, and the calamistruni is brought immediately 

 beneath the spinners, at right angles with the line of the abdomen. By a 

 slight extension of the joints of the posterior legs the calamistrum is directed 

 backwards across the diverging extremities of the spinners, which it touches 

 in its transit, and is restored to its former position by a corresponding degree 

 of contraction in the joints. In proportion to the continuation of this process 

 the inflected lines of the flocculus are produced, the spider making room for 

 them as they accumulate by elevating and at the same time advancing the 

 abdomen a little, which it effects by slightly extending the joints of the third 

 pair of legs and contracting those of the first and second pairs. When the 

 requisite quantity of inflected filaments is obtained, the spider again applies 

 its spinners to one of the glossy lines and attaches the flocculus to it. In this 

 manner it proceeds with its labours, occasionally employing both calamistra, 

 till the snare is completed. The modus opei'andi appears to be this. The 

 points of the lower row of spines in passing over the extremities of the spinners 

 draw from them lines which run into numerous flexures in consequence of 

 not being kept fully extended, and the purpose subserved by the spines of the 

 upper row is the detachment of these lines from the spines of the lower row 

 by a motion upwards f. 



If the metatarsus of one of the posterior legs of Ciniflo ferox, a spider of 



* Transactions of the Linnsean Society, vol. xvi. p. 476 ; vol. xviii. p. 224, note*, 

 t Ibid. pp. 471-475 ; vol. xviii. pp. 224, C06. 



