. American spiders and their spinning work. A natural history of the orbweaving spiders of the United States, with special regard to their industry and habits. Spiders. THE SPINNING ORGANS. 49 genera Epeira, Tetragnatha, Linypliia, Theridium, Agalena, and many others, they are generally large, more numerous and minute on the an- terior spinnerets than on the posterior and middle ones. The last are the most sparingly supi)lied with them, and in the case of Scgcstria senoculata each has only three large spools at its extremity. On each of the posterior spinnerets Mr. Underhill found three spigot
. American spiders and their spinning work. A natural history of the orbweaving spiders of the United States, with special regard to their industry and habits. Spiders. THE SPINNING ORGANS. 49 genera Epeira, Tetragnatha, Linypliia, Theridium, Agalena, and many others, they are generally large, more numerous and minute on the an- terior spinnerets than on the posterior and middle ones. The last are the most sparingly supi)lied with them, and in the case of Scgcstria senoculata each has only three large spools at its extremity. On each of the posterior spinnerets Mr. Underhill found three spigots differing in character from those of tlie anterior spinnerets. Fig. 40, sp. Their form and size as com])ared with the spools of the anterior pyriform glands () is shown in the figure. These spigots are evidently the ones comiected with treeform glands; which glands Underhill estimates at five mil- limetres (three-twentieths to four-twen- tieths of an inch) in length, while the common pyriform glands are about one millimetre (one one-hundredth of an inch). The ducts which connect those glands and spigots are shown at , Fig. 45, where their covering of curious globular cells is indicated. These cells according to Underhill are so slightly attached as to be easily rubbed off dur- ing manipulation. He had not seen anything analogous to this gland on any other genus than Epeira except the exotic Orbweaver Nephila; and for this reason conjectured that through these spigots and from this gland the viscid beading of the Orbweaver's spirals may be drawn. Mr. Underbill has stated that in a large Tcgenaria domcstica, one one-lum- fig. 45. onc posterior, p, and two middle, m dredth of an inch is the average length of the silk duct. On the posterior pair of spinnerets are about sixty tubes; on the middle pair, although the spinnerets are smaller, about eighty. The spools on these two pairs arc alike, but they differ in shape from those of the anterior pair and are much larger. The
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectspiders, bookyear1889
