THE SPINNING ORGANS. 49 
genera Epeira, Tetragnatha, Linyphia, 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 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 these 
spigots and from this gland the viscid 
beading of the Orbweaver’s spirals may 
be drawn. 
Mr. Underhill has stated that in a 
large Tegenaria domestica, one one-hun- Fic. 45. One posterior, P, and two middle, M, 
‘ aa Se nan spinnerets of Epeira diademata. (After Under- 
dredth of an inch is the ave Bee length hill.) p.sf, posterior spinning field; tr.d, ducts 
of the silk duct. On the posterior pair of the treeform glands; py.g, pyriform glands 
A . . with their ducts, du; m.ss, the middle spinning 
of spinnerets are about sixty tubes; on — spools in clusters. 
the 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 spinnerets. 
Spools Blackwall also made the discovery that the number of spools 
Vary with : ; : fom 
Age. varies with the age of the female. In specimens of Drassus 
ater, which had attained nearly a third of their growth, they 
amounted to five or six. In others, which were two-thirds grown, to 
six or seven. In adults which had acquired their full complement, they 
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