1889.] NATURAL SCIENCES OF PHILADELPHIA. 183 



spider tak/s its position upon the handle or trapline of its little ray- 

 formed web, holding between its fore feet and the third pair of feet 

 a coil of slack line. When an insect strikes its snare it quickly 

 unlooses its fore feet, and the web shoots forward the distance of the 

 coil of slack line. It is then rapidly gathered up again and succes- 

 sively snapped in this wise until the insect is thoroughly entangled. 



Now, this same method of springing its net and trapping its prey 

 is habitual with Therldiosoma radio-sum. Its web may be said to be 

 composed of a series of rays somewhat resembling the orb sector of 

 the Triangle spicier. The handles or traplines of these rays are, 

 however, all centered upon a common thread or trapline, which the 

 little weaver holds within her feet. She has the power of springing 

 or snapping off all these combined concentrics at once ; or, if she so 

 choose, to spring one or more of them at a time. She thus in this 

 remarkable and essential particular resembles the Triangle spider 

 in her habit. Had the spiral lines of her web proved to be of the 

 same character as those of the Triangle spicier, this peculiarity of 

 combining the rays upon a central point might not have seemed 

 so remarkable ; but when it is found that the spiral lines are covered 

 with beads entirely after the manner of true Orbweaving spiders, 

 the combination becomes very striking and remarkable indeed. 



Many Orbweavers do use a trapline in connection with their 

 webs. This is almost invariably the custom with those which make 

 an orb having in the upper part an open segment, as is the case 

 with Epeira triaranea, Epeira thaddeus and generally with the 

 species of the genus Z'dla. But this trapline, while it is attached to 

 the center of the orb, and assists to hold the various converging 

 lines taut, has simply these two uses : first, it is used as a telegraphic 

 line along which pass the vibrations of the entangled insect, and 

 which are thus communicated to the owner of the snare who oc- 

 cupies a position in a little den just above and beyond her domain. 

 Second, the trapline serves as a gangway along which ihe spider 

 runs first to the center of her orb and then to the point where her 

 prey happens to be entangled. None of these Orbweavers, however, 

 make any such use of their traplines as that which has been described 

 as habitual to the Triangle and Ray spiders. Perhaps one may 

 not Jie able to suggest a method by which these variations have been 

 originated, but at all events, it must be conceded that the fact, which 

 is in this communication placed beyond question, as to the viscid 

 character of the spiral lines of the Ray spider's snare, certainly 

 reveals a connecting link between two forms of spinningwork, 

 namely that of the Triangle spider and that of the typical geometric 

 Orbweaver, which had heretofore been supposed to stand at the 

 opposite extremes of the spinningwork of a great family, without 

 any known connection between the two. 



