and CEconomy of the Araneidea. 241 



the ascent of air highly rarefied ; and directions intermediate be- 

 tween these two will, in general, depend upon the composition of 

 forces. When the horizontal and vertical currents are equal in force, 

 the line of direction will describe an angle of 45° nearly with the 

 plane of the horizon ; but when their forces are unequal, the angle 

 formed with that plane will be greater or less as one current or the 

 other predominates. 



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

 spinners by a current of air appears to be this. As a preparatory 

 measure, the spinning mammulse are brought into close contact, and 

 viscid matter is emitted from the papillas ; they are then separated 

 by a lateral motion, which extends the viscid matter into fine fila- 

 ments connecting the papillae ; on these filaments the current im- 

 pinges, drawing them out to a length which is regulated by the will 

 of the animal ; and on the mammulae being again brought together 

 the filaments coalesce and form a compound line. 



Many intelligent naturalists entertain the opinion that spiders can 

 forcibly propel or dart out lines from their spinners ; but when placed 

 on twigs set upright in glass vessels with perpendicular sides contain- 

 ing a quantity of water sufficient to immerse their bases completely, all 

 the efforts they make to effect an escape uniformly prove unavailing 

 in a still atmosphere. However, should the individuals thus insu- 

 lated be exposed to a current of air either naturally or artificially 

 produced, they immediately 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 re- 

 gaining their liberty. If due precaution be used in conducting this 

 experiment, it clearly demonstrates that spiders are utterly incapable 

 of darting lines from their spinners, as they cannot possibly escape 

 from their confinement on the twigs in situations where the air is un- 

 disturbed, but in the agitated atmosphere of an inhabited room they 

 accomplish their object without difficulty. Similar means are fre- 

 quently employed by spiders in their natural haunts for the pur- 

 poses of changing their situation and fixing the foundations of their 

 snares. 



The webs named gossamer are composed of lines spun by spiders, 

 which on being brought into contact by the mechanical action of 

 gentle airs adhere together, till by continual additions they are ac- 

 cumulated into irregular white flakes and masses of considerable 

 magnitude. Occasionally spiders may be found on gossamer- webs 

 after an ascending current of rarefied air has separated them from 

 the objects to which they were attached, and has raised them into 

 the atmosphere ; but as they never make use of them intentionally in 

 the performance of their aeronautic expeditions, it must always be 

 regarded as a fortuitous circumstance*. 



* Transactions of the Linnaean Society, vol. xv. p. 449-459. Researches in Zoo- 

 logy, p. 229-252. 



