54 PROCEEDINGS OF THE AMERICAN ACADEMY 



found in large geometrical web-, two, three, or four feet in diameter, 

 stretched between shrubs or trees, and often high up among the pines, 

 so as to be out of reach. The webs are strong and of a yellow color ; 

 and, as with most species of geometrical spiders, the concentric circles 

 are elastic and studded with numerous viscid globules, while the radii 

 and other parts of the framework are composed of dry and inelastic 

 silk ; but with this species the distinction between these two portions of 

 the web consists not only in the viscidity of the former, but also in the 

 color ; for while most of the concentric circles are of a bright yellow or 

 golden hue, the radii and stay-lines, and also every eighth or tenth circle 

 (the number varies in different individuals), are white or silver-colored. 

 The circles are very near together in proportion to the size of the in- 

 sect, being only one third or one fourth of an inch apart. 



As might be inferred from these facts, but which, so far as I know, 

 has .never before been observed, this spider not only has the power of 

 resrulatina: the size of its thread, — according as one or two, or three or 

 four of its spinnerets are pressed upon the surface from which the line 

 is to extend, or as a greater or less number of the spinnerules in any 

 one spinneret are employed, — but can also use in the construction of its 

 web either the white or the yellow silk at will ; for of its two principal 

 pairs of spinnerets, one, the anterior, yields the yellow, while the other 

 or posterior pair yields the white silk. Of this I satisfied myself by 

 carrying the thread from the anterior pair of spinners upon one part 

 of a spindle, and that from the posterior pair upon another part, guid- 

 ing them with pins while the spindle was in motion ; the result being 

 the formation of two circles of silk, one of a golden, the other of 

 a silver color, as in one of the specimens exhibited ; moreover, if 

 while both threads are being drawn out, they are slackened, the lower 

 silver thread will wrinkle and fly up, being inelastic ; while the other 

 will contract and, within certain limits, preserve its direction. 



There is a corresponding difference in the color of the glands which 

 secrete the gum of which the silk is formed ; one set, the more numer- 

 ous, being yellow, and the other white. 



The manner in which the spider deposits the globules of gum on 

 the circles which she wishes to be viscid is not yet explained ; at any 

 rate this same yellow silk, when either reeled from the body of the 

 spider, or when employed in the formation of its cocoon, is dry and 

 much less elastic than that of which the concentric circles are composed. 



The evolution of the silk from the spider is almost wholly a mechan- 



