THE SPINNING ORGANS. 



49 



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genera Epeira, Tetragnatlui, Linyphia, Theridium, Agalciia, and man}' 

 others, they are generally large, more numerous and mimite on the an- 

 terior spinnerets than on the posterior and middle ones. The last are the 

 most sparingly supplied with them, and in the case of Segestria 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 the anterior spinnerets. Fig. 46, sp. 

 Their form and size as compared with the spools of the anterior pyriform 

 glands (ss.p) is shown in the figure. These spigots are evidently the ones 

 connected 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 tr.g, 

 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 tliese 

 spigots and from this gland the viscid 

 beading of the Orbwcaver's spirals may 

 be drawn. 



Mr. Underhill has stated that in a 

 large Tegenaria domestica, one one-hun- 

 dredth of an inch is the average length 

 of the silk duct. On the posterior pair 

 of spinnerets are about sixty tubes; on 

 tlie middle pair, although the spinnerets 

 are smaller, about eighty. The spools on these two pairs are alike, but 

 they differ in shape from those of the anterior pair and are much larger. 

 There are nearly two hundred and twenty spools on the anterior pair, thus 

 making altogether three hundred and sixty on the six s[)innerets. 

 Blackwall also made the discovery that the nund)er of spools 



in.ss 



Fic. 45. One posterior, P, and two middle, M, 

 spinnerets of Epeira diademata. (After Under- 

 bill.) p.sf, posterior spinning field ; tr.d, ducts 

 of the treeform glands ; py.g, pyriform glands 

 with their ducts, du ; ni.ss, the middle spinning 

 spools in clusters. 



Spools 



Affe varies with the age of the female. In s[UTiiiK'ns of Drassus 



ater, which had attained nearly a third of their growth, they 



amounted to five or six. Tn others, which were two-thirds grown, to 



six or seven, lu adults which had ac(piired their full complement, they 



