8 



motion of the calamistrum to produce them. It seems more 

 probable that the structure of these strands is such that they 

 curl naturally, like the hair of a negro. 



The most complicated hackled band that I have observed 

 is that made by Filistata hibernalis, which is a common house 

 spider in the Southern United States. 



Under natural conditions the web of this spider is so quickly 

 injured by insects and obscured by dust that its plan of structure 

 is not easily seen. But this is well shown in some webs that 

 were built by spiders in confinement in my laboratory (PI. V, 



fig- 9)- 



The most characteristic feature of this web is a series of 



radiating lines, which consist of a double plain thread supporting 



a looped hackled band. In making these lines the spider spins 



a thread of plain silk, which consists of several parallel strands, 



from near the centre of the web to a distant point, where it is 



fastened by an attachment disk ; the spider then returns to the 



starting-point, spinning as it goes another similar thread closely 



parallel to the first. Upon these two threads, which serve as a 



foundation, are fastened afterwards loops of a hackled band. 



This doubled supporting line and the loops of the hackled band 



can be seen with the unaided eye. 



A small section of one of the radiating lines is shown greatly 

 enlarged by Fig. 8. This picture is from a photomicrograph, 

 and is not as perfect as could be desired ; for with the high 

 magnification necessary to see the details it was impossible to 

 get all parts of a loop in focus at once. 



Four kinds of silk enter into the formation of this remarkable 

 structure. First, the doubled supporting line. Second, the 

 primary looped threads ; there are two of these, and they form 

 the axis of the hackled band ; they are extremely elastic. Third, 

 the secondary looped threads ; there is one of these, supported 

 by each of the two primary looped threads ; each of the secon- 

 dary looped threads forms a very regular series of loops, each 

 of which is fastened by one end to the primary looped thread ; 

 this secondary thread is not looped around the primary thread, 

 as it appears to be, but is merely fastened to one side of it by 

 viscid silk. Fourth, the viscid silk ; this is an amorphous sheet, 

 which fills the spaces between the loops of the secondary looped 



