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. 



