156 MR. J. BLACKWALL ON SOME REMARKABLE EACTS 



disturbed. However, should individuals thus insulated be ex- 

 posed to a current of air, either naturally or artificially produced, 

 they instantly turn the abdomen in the direction of the breeze, 

 and emit from the spinners a little of their viscid secretion, which, 

 being carried out in a line by the current, becomes connected with 

 some object in the vicinity, and affords them the means of regain- 

 ing their liberty. This line uniformly moves in the direction and 

 with the velocity of the stream of air ; but if, while proceeding 

 from the spinners, it be subjected to the action of a lateral or 

 opposing current, it immediately becomes deflected from its course 

 by the new impulse thus imparted to it. 



I may here remark that numerous species belonging to various 

 genera of spiders, — Drassus ater, Cinijlo similis, Ergatis latenSy 

 Tegenaria civilis, Ccelotes saxatilis, Dysdera erythrina, and Oonops 

 pulclier, for example, — though provided with highly organized spin- 

 ners, yet do not appear to be endowed with the instinct to avail 

 themselves of a current of air for the purpose of transmitting 

 their lines to a distance. 



The manner in which the lines of spiders are drawn out from 

 the spinners by a current of air admits of an easy explanation. 

 As a preparatory measure, the extremities of the spinners are 

 brought into contact, and viscid matter is emitted from the pa- 

 pillae ; they are then separated by a lateral motion, which extends 

 the viscid matter into filaments connecting the papillae ; on these 

 filaments the current impinges, drawing them out to a length 

 which is regulated by the will of the animal, and on the ex- 

 tremities of the spinners being again brought together, the fila- 

 ments coalesce and form one compound line. 



The only legitimate deduction from the foregoing experiments, 

 which have been frequently repeated under every variety of cir- 

 cumstances likely to aifect the result, ajipears to be that the lines 

 produced by spiders are not propelled from the spinners by any 

 physical power possessed by those animals, but that they are in- 

 variably drawn from them by the mechanical action of external 

 forces. 



§ 2. 



The importance of the greatly diversified form of the remark- 

 able organs connected with the radial and digital joints of the 

 palpi of male spiders, in affording valuable specific characters in 

 numerous cases in which species so closely resemble each other in 

 size, colour, and economy as scarcely to be distinguished except 

 by miiiute differences in their external structure, is beginning to 



