1881.] NATURAL SCIENCES OF PHILADELPHIA. 431 



across country roads of from thirty to forty feet. Many of these 

 lines he Iiacl seen carried by the wind directly from the spiders' 

 spinnerets, had observed the entanglement, had seen the animal 

 draw the threads taut and then cross upon them. That all the 

 lines were similarly formed and used he had no doubt. 



It was more difficult to detei'mine the other question, viz.: 

 Whether the lines used for the foundations of orb-webs were 

 formed in the same way. Undoubtedly, such lines are often made 

 precisely as asserted by M\-. Cambridge. Dr. McCook had many 

 times observed this ; he had seen an orb-weaver after traversing a 

 considerable space by a series of successive bridge-lines settle 

 upon a site between the forked twigs of a bush and carry her 

 foundation lines around in the manner described But, on the 

 other hand, he was prepared to say that the air-laid bridge-lines 

 were also used for the foundations or frames of orbs. 



1. First, he had observed that the hours in the evening at 

 which the greatest activit}' in web-weaving began, were those in 

 which also began the formation of the bridge-lines. The latter 

 action quite invariably preceded the former. 



2. Again, a study of the foundation lines of many webs gave 

 more or less conclusive evidence that they were laid by the aid of 

 air currents. For example, the webs of some species, as Acrosoma 

 miitra.ta^ A. spiyiea and A. rugosa,, Avere frequently found strung 

 between young trees separated by two or three 3'ards. That these 

 builders might have dropped to the ground, crept over wood, grass- 

 and drj' leaves carrying the thread in the free outstretched claw,, 

 is, perhaps, not impossible, but did not seem at all probable to the 

 speaker, although short spaces over smooth surfaces might well 

 be cleared in this way. One web he found spun upon lines 

 stretched from the balustrade of a bridge that spans a deep glen 

 in Fairmount Park, to the foliage of a tree that springs out of 

 the glen at least twenty-five feet below. Unless foundations were 

 formed by line-bridging the interspace of a 3'ard or more^it must 

 be inferred that the spider had dropped from the balustrade to the 

 glen, crossed the interval to the trunk of the tree, ascended it, 

 and having made the detour ol nearly sixt}^ feet to the point 

 direetl}^ opposite that from which she started, drawn her long line 

 taut, and so completed her foundation. Dr. McCook thought that 

 such a supposition could not be entertained, and it was clear that 

 a breeze carried the line across from the spider's spinnerets. 



Even stronger examples of circumstantial evidence were noted. 

 Very many webs of Tetragnatha extensa and T. grallator were 

 seen spread upon bushes overhanging pools and streams of 

 water ; others were seen stretched between separated water-plants, 

 or from such plants to the shore. Either the foundation lines 

 were borne by air currents, or the spiders must have crossed upon 

 the water, carrying their lines. The latter supposition is not 

 wholly untenable, the speaker thought, but would hardly be raised 

 by any one who had studied the spinning habits of the creature. 

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