CONSTRUCTION OF AN ORBWEB. 



63 



Black 

 ■wall. 



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

 have seen the animal draw the threads taut and then cross u^Don them. 

 That all tlie lines are similarly formed and used I have no doubt. 



Mr. Tcrby, in a paper contributed in 18G7 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 i)oint. 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.i Black wall also had ob- 

 served as much 

 and gives a brief 

 and accurate de- 

 scription. The manner, he 

 says, in which the lines of 

 spiders are carried out from 

 the sjiinners by a current of 

 air appears to be this : as 

 a preparatory measure, the 

 spinnerets are brought into 

 close contact and viscitl 

 matter is emitted fro7ii the 

 s[)inning spools. They are 

 then sejiarated Ijy a lateral 

 motion, which extends the 

 vi.scid 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 si^innerets being again brought to- 

 gether the filaments coalesce and form one compound line.^ 



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 



^ M. F. Terby, sur les proc^d^s qu'emploient les araigii^es pour relier des points eloignfe par 

 un f]l. Bull. r.\[-adeniie Royale de Belfjique, 1867, jjage 274, sq. 

 ^ Researches in Zoology, page 269. 



Fi(i. 61. A colony of spiders domiciled over water. 



