i 



170 PROCEEDINGS OF THE ACADEMY OP [188L 



pairs of legs, and SI is the coil or slack-line between these and the 

 fore pairs (1 and 2), or simply between the pair of fore-legs, 1 and 

 2. As the spider does not exceed one-eighth of an inch in body 

 length, and the position of the snare is within cavities and inter- 

 stices of rocks, where the light does not bring out the delicate 

 tracery of the fine webs, the observation of these and other points 

 of like character, is a matter of some difficulty. But, although 

 the exact relations of the coil to the feet were sometimes in doubt, 



and indeed seemed to vary somewhat, 

 the existence of the coil and its general 

 relations were determined beyond doubt. 

 It is also certain that the slack-line 

 sharply uncoils and straightens when 

 the spider releases her grasp upon the 

 trap-line, and that the web unbends and 

 shoots quickly forward. It is instantly 

 changed from the bowed or conical form 



of figs. 4 and 5 to the circular plane of 

 FIG 8 -Ray spider (greatly ea- ^ ^ ^^^ ^ 

 larged) in position on taut snare. ° 

 To show the slack-line coil, SI. The following points, howcvcr, long 



evaded my observation, before webs 

 were found which presented the conditions for successful study. 

 But at last I was well satisfied, although I hope for further and 

 fuller verification during, the present summer. The " springing " 

 of the snare is caused by the sudden releasing of the trap-line 

 from the fore-feet^ instead of the hind-feet, as with the Triangle 

 spider. The polarity of the two arachnids relative to their webs 

 is reversed, Hyptiotes having her fore-feet, but Radiosa her hind- 

 feet towards the web. The slack-line is therefore coiled between 

 the two fore-feet or between the fore and hind-feet of Radiosa, 

 but between the two hind pairs (as a rule) of Hyptiotes. 



A glance at fig. 6, b, will suggest the manner in which Hj'ptiotes 

 is affected when her two hind feet are released from the trap-line. 

 The coil, SI, straightens, and the whole body of the spider shoots 

 forward. If now we turn to Radiosa, as represented at fig. 8, or 

 again, as shown somewhat better at fig. 9, we observe that if the 

 fore-feet ,1,2, fig. 9, are released suddenly from the trap-line, T, 

 the whole body shoots backward, although still toward the snare, 

 as with Hyptiotes. This was the action which I observed. 



The determination was finally accomplished by first carefully 



