HARDWICKES SCIENCE-GOSSIP. 



181 



are little funnel-shaped tubes (a and b, fig. 120) from 

 which the silk is emitted, and which I call " silk- 

 tubes," being ignorant of their proper name. The 

 spinnerets lie in pairs, and are naturally divisible 

 into two "sets," an upper and a lower. There are 



Fig, 118. Web of Tegenaria domeiUea, x 150. aa, first threads; 

 bb, second ditto ; ec, third ditto. 



Fip. 119- Under Spinneret, with glands attached, of Tegenaria 

 domestica, x 38. a, common silk-tubes; bb, ducts; cc, 

 glands; d, silk-tube of unusual size. 



two pairs in the upper set, one above the other, 

 which I therefore name the first and second pairs ; 

 the one pair in the lower set being distinguished 



as the third pair. The first spinnerets, i.e. the 

 spinnerets of the first pair, have two joints, and their 

 silk-tubes are situated sometimes on the end of the 

 second joint, and sometimes irregularly down its 

 inner side. The second spinnerets have but one 

 joint. They are smaller than the first, and have the 



Fig. 120. a and b, silk-tubes of first 

 and third spinnerets of T, domestica. 



Fig. 121. Silk-tube, duct, and 

 (iland of the first spinnerets 

 of T. domestica, x 38. 



Fig. \'i2. Gland of third spin- 

 ners, a, gland ; b, bag or 

 case; rr, coating of epithe- 

 lial cells. 



silk-tubes on and around the ends. The construc- 

 tion of the third pair differs a little from that of 

 the other two. Like the first they have two joints, 

 but the basal joint is always much larger than the 

 terminal, which is very short. Their silk-tubes are on 

 a retractile plate at the end of the second or terminal 

 joint, which, when not in use, is drawn inwards until 

 the tips of the silk-tubes are nearly level with the end 

 of the spinneret. This plate has a thickened] rim, 

 and on the interior margin, where the rim is 

 broadened for the purpose, are a'few holes and two , 

 silk-tubes of unusual size. The exact use of these 

 1 have been unable as yet to determine. The spin- 

 nerets of a spider are mobile, and their movements 

 are effected by longitudinal muscles. 



