CONSTRUCTION OF AX ORBWEB. 



63 



tlu- 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 have no doubt. 



Mr. Terby, in a paper contributed in 1867 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 

 ' er y ' 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 the 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. 1 Black wall also had ob- 

 served as much 

 Black- i - -i i- 



wall anc * g lves a brief 



and accurate de- 

 scription. The manner, he 

 says, 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 

 spinnerets are brought into 

 close contact and viscid 

 matter is emitted from the 

 spinning spools. They are 

 then 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 which is regulated 

 by the will of the animal, and on the spinnerets being again brought to- 

 gether the filaments coalesce and form one compound line. 2 



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

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

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



1 M. F. Terby, sur les proc&les qu'emploient les araignees pour relier des points eloignes par 

 un fil. Bull. 1' Academic Royale de Belgique, 1867, page 274, aq. 



2 Researches in Zoology, page 2iv. 



FIG. 61. A colony of spiders domiciled over water. 



