302 HOMES ■VriTIIOUT HANDS. 



Mr. Blackwell has the following remarks upon the stractiire of 

 the threads : — " As the radii are unadhesive, and possess only a 

 moderate share of elasticity, they must consist of a different 

 material from that of the viscid spiral line, which is elastic in an 

 extraordinary degree. Now, the viscidity of this line may be 

 shown to depend entirely upon the globules with which it is 

 studded, for if they be removed by careful application of the 

 finger, a fine glossy filament remains, which is highly elastic, but 

 perfectly unadhesive. As the globules, therefore, and the line 

 on which they are disposed, differ so essentially from each other 

 and from the radii, it is reasonable to infer that the physical con- 

 stitution of these several portions of the net must be dissimilar. 



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 Upeira in the construction of their snares. The mean dis- 

 tance between two adjacent radii in a net of this species, is 

 about seven-tenths of an inch ; if therefore the number seven 

 be multiplied by twenty, the mean number of viscid globules 

 which occur on one-tenth of an inch of the elastic spiral line, 

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

 mean number of globules deposited on seven-tenths of an inch 

 of the elastic spiral line. This product multiplied by twenty- 

 four, the mean number of circumvolutions described by the elastic 

 spiral line, gives 3,360, the mean number of globules contained 

 between two radii ; which, multiplied by twenty-six, the mean 

 number of radii, produces 87,360, the total number of viscid 

 globules in a finished net of average dimensions. 



A large net, fourteen or sixteen inches in diameter, will be 

 found by a similar calculation to contain upwards of 120,000 

 viscid globules, and yet Upeira apoclisa will complete its snare 

 in about forty minutes if it meet with no inteiTuption." 



These calculations will serve to show the elaborate nature of 

 the webs which we see constantly in our gardens, as well as 

 their value to the architect. The secretion of the liquid from 

 which the lines proceed is a work of time, so that if a spider is 

 forced to spin several nets in rapid succession, it loses all its silk 

 and cannot make a web. To wait until a fresh supply should 

 be secreted would be a terrible privation, and moreover, the 

 want of food would stop the secretion, so that the spider has no 



