SPINNING APPARATUS OF GEOMETRIC SPIDERS. 37 



such spiders — and such only — on whose threads the viscid 

 matter has been observed. On dissecting out the various 

 glands from a spider, isolating them on slides^ and crushing 

 them, I found that the contents of the Aggregate glands 

 retained their viscidity the longest. Evidence was also sought 

 from histological changes in the glands themselves before and 

 after web -spinning, and though a much larger series of obser- 

 vations would be necessary to afford trustworthy results, 

 alterations similar to those known to occur in active serous 

 glands seemed to be taking place (figs. 19 and 20). 



This would show that the Aggregate glands are used in 

 spinning the web, in which case they must furnish the viscid 

 matter, all the other structures being accounted for. 



The unsafe nature of such indirect evidence is, however, 

 freely admitted, but it may be pointed out that the certainty 

 which now exists with regard to some of the glands gives 

 greater probability of the true function being allotted to the 

 remainder. 



One other web structure remains to be briefly discussed. 

 Foundation lines are attached to surrounding objects, and 

 ordinary non-viscid lines are glued to one another by little 

 patches of silk which we may call attachment discs (Haft- 

 scheibe, Apstein). The spider rubs its anterior spinnerets 

 against a surface, emitting silk from the Piriform glands, and 

 upon walking away a line is drawn out from the spinnerets. 



I have been best able to study these structures in a small 

 bottle in which a spider was obliging enough to deposit its 

 eggs, fixing the cocoon in its place by a multitude of cross 

 threads fixed to the sides of the bottle at their ends, and to one 

 another where they intercrossed. Their appearance is given in 

 figs. 16 — 18. It was this structure which led to the belief in 

 the highly compound nature of the spider^'s line. 



