CONSTRUCTION OF AN OllBWEB. 



63 



Black 

 ■wall. 



the wind directly from spiders' spinnerets, have observed the entanglement, 

 have seen the animal draw the threads taut and then cross upon them. 

 That all the lines are similarly formed and used I liave no doubt. 



Mr. Terby, in a paper contributed in 1807 to the Royal Academy of 

 Belgium, makes a number of intelligent and accurate observations upon the 

 habit of spiders to throw out their floating threads in order to 

 secure passage from point to point. He demonstrated by numer- 

 ous experiments that these threads could not be projected by the power of 

 the spider without the aid 

 of tlie wind. I regret that 

 I only happened to fall 

 upon this paper after the 

 completion of my manu- 

 script, so that I can insert 

 here but a brief allusion to 

 it.^ Black wall also had ob- 

 served as much 

 and gives a brief 

 and accurate de- 

 scription. The manner, ho 

 says, in which tlie lines of 

 spiders are carried out from 

 the spinners by a current of 

 air ap})ears to be this : as 

 a preparatory measure, the 

 spinnerets are brought into 

 close contact and viscid 

 matter is emitted from the 

 spinning spools. They are 

 'til en separated by a lateral 

 motion, which extends the 

 viscid matter into fine fil- 

 aments, connecting the 

 spools. On these filaments 

 the current of air impinges, 

 drawing them out from the spinnerets to a length wliich is regulated 

 by the will of the animal, and on the si>innerets being again brought to- 

 getlier the filaments coalesce and form one comimund hne.^ 



It is a more difficult matter to determine whether lln' lines used for the 

 foundations of orbwebs are formed in the same way. 1 have seen an orb- 

 weaver, after traversing a considerable space by a series of successive bridge 



' M. F. Tc'rl)y, siir les proct'drs i|ii'('ni|il(iicnt Ics aniiuMiri'S iMHir- iclicr ilcs |M.iiits cldij.'iii's i-ar 

 nil fil. I'.iill. rAcadrinic Royalc df l'.c'l'ii(HH", iSC.?, pa.Lrc -74, S(|. 

 - K(_'!<c'arclu'8 in Zoology, \>ii'^e !'()!». 



Fii;. 61. A colony of spiders domiciled over water. 



