178 



AMERICAN SPIDERS AND THEIR SPINNINGWORK. 



Fig. 165. Spinning organs of Clubiona, 

 showing the cribellum, cb. P, pos- 

 terior ; m, middle ; a, anterior spin- 

 nerets ; ca, calamistrum. (After 

 Blackwalh) 



an old fashioned spinning wheel, and is apparently used to separate into 

 a flossy mass the threads of silk as they issue from the spinning glands. 

 Bertkau, in an article on the cribellum and calamistrum, has shown cer- 

 tain secreting glands at the ends of the fine tubes which have their 

 outlets in the former organ. It is not improbable, in view of this dis- 

 covery, that the viscidity of the flocculent spirals 

 of Uloborus and other spiders possessing this 

 organ is caused in some measure by a slight 

 secretion from these glands. 



It is the possession of cribellum and cala- 

 mistrum by Uloborus and Hyptiotes which has 

 led various arachnologists to separate 

 Calamis- ^.j-^ggg ^^^.^ genera from the Orbweavers. 



Cribellum Emerton, for example, following Black- 

 wall, Keyserling, and Bertkau, assigns 

 them to the Clubionidte. Without entering at 

 length into the reasons, based upon structure, for 

 dissenting from this opinion, I have felt con- 

 strained, on the grounds of their spinningwork 

 alone, to place both these genera among the Orbitelarias, where indeed sucli 

 a distinguished systematic arachnologist as Professor Thorell has already 

 placed them, and continues to keep them, notwithstanding all the objec- 

 tions that have been advanced l^y the able naturalists who have espoused 

 the other view. 



Mr. Emerton has made some studies of the web of Uloborus Walck- 

 enaerius, the common species of Northern Europe. I reproduce his figure 

 (Fig. 1G7), which represents an unfinished web of this species 

 SDecSs^^ seen in France. It shows the central part still occupied by the 

 preliminary spirals or scaffolding, while the outer part is covered 

 with curled threads, and the smooth spirals cut away (or not yet inserted), 

 leaving thickened spots or ribbons on the rays. In the finished web most 

 of the spirals pass regularly around, but the outer ones are often more or 

 less irregular, as in Epeira webs, according to the shape of the space in 

 which the web is made. 



According to this author, Uloborus, after inclosing her eggs in the co- 

 coon, becomes careless about her web, 

 and repairs it only enough to keep the 

 cocoons in place, so that many imper- 

 fect and irregular webs are found at 

 the cocooning season. The only web 

 of Uloborus plumipes seen by Emerton 

 was imperfect from the above cause, but was eviiUnilly the remains of a. 

 nearly round web, the rays meeting somewhat nearer the ui)per than the 

 lower edge. 



Fig. 166. Curled thread of Clubiona. 

 (After Staveley.) 



