M r. Blackwall on the Functioris and CEconorny 0/ Araneidea. 221 acid. But whatever be the case with regard to the origin of the cuticle, I must certainly protest most decidedly against Hartig's representation that the cuticle consists of three layers, and that the membranes penetrating into the interior of the leaf are a continuation of only one of these layers, the innermost, and that they form hollow, vessel-like tubes in the intercellular passages, since I have not observed a single circumstance that would afford a confirmation of any one of these statements. XXVIII. — Researches into the Structure, Functions and (Eco-nomy of the Araneidea. By John Blackwall, F.L.S.* In essaying to give an epitome of some investigations recently made in this country relative to the organization, physiology and oeconomy of the Araneidea^ I shall endeavour to accomplish the undertaking in as compendious a manner as may be deemed compatible with a perspicuous statement of the various facts to be detailed, distinguish-ing those already before the public from such as are not by refer-ences to the works in which they have appeared. Without further preface, I proceed to the consideration of those remarkable appendages termed scopulce or brushes, with which the tarsi of numerous species of spiders are provided. This apparatus, consisting of coarse, compound, hair-like papillae either distributed along the inferior surface of the tarsi or situated immediately below the claws at their extremity, bears a close analogjr to the tarsal cushions of insects, enabling its possessor to ascend the perpendicular surfaces of highly polished bodies and even to adhere to smooth objects in an inverted position by the emission of a viscous secretionf. The different plans according to which the papillae are disposed upon the tarsi are respectively represented by two common British spiders, Drassus sericeus and Salticus scenicus. Some of the spiders belonging to the families Theridiidce and Epei" ridce 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 Epeirce indi-genous to Great Britain, exhibit this structure to advantage under the microscope ; they have, besides, a strong, moveable spine, in-serted 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 im-portant 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 * From the Report of the Meeting of the British Association held at York 1844. + Transactions of the Linnaean Society, vol. xvi. pp. 768, 769. Researches in Zoology, p. 289.
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