Structure and Economy of Spiders. 477 



instruments employed by the Geometric Spiders for the purpose 

 of suspension, it is obvious why they usually direct their heads 

 downwards when they occupy the centre of their nets. 



As several difficulties present themselves in the prosecution 

 of these researches, occasioned chiefly by the impracticability 

 of comprising all the claws in one distinct view ; and as I have 

 not yet succeeded in procuring instruments of sufficient delicacy 

 to enable me to accomplish the dissection of exceedingly minute 

 objects under the microscope, I cannot completely satisfy myself 

 at present whether the number and arrangement of the addi- 

 tional claws are uniformly the same on the feet of such spiders 

 as I have ascertained to be supplied with them ; though as 

 regards the larger species I am thoroughly convinced that this 

 is the case, and I have reason to think that it will ultimately 

 prove to be so with the rest. In pursuing the inquiry, these 

 particulars, of course, will claim my especial attention. 



It is not at all surprising that the Geometricians, which em- 

 ploy their feet in the fabrication of complicated nets, should 

 have them more amply provided with claws than those species 

 which use theirs principally as instruments of progression. An 

 estimate of the number of viscid globules distributed on the 

 elastic spiral line in a net of Epeira apoclisa of a medium size, 

 will convey some idea of the elaborate operations performed by 

 the Geometric Spiders in the construction of their snares*. The 

 mean distance between two contiguous radii in a net of this 

 species, is about seven tenths of an inch ; if, therefore, the 

 number 7 be multiplied by 20, the mean number of viscid glo- 

 bules which occur on one tenth of an inch of the elastic spiral 

 line at the ordinary degree of tension, the product will be 140, 



*For a circumstantial account of the manner in which the Geometric Spiders con- 

 struct their nets, see the Zoological Journal, vol. v. p. 181. et seq. 



the 



