318 HOMES "WITHOUT HANDS. 



It may perhaps be necessary to remark that the threads with 

 which the spiders make their webs are in some respects similar to 

 those which are produced by various caterpillars, and in other 

 respects are exceedingly dissimilar. In both cases the threads 

 are formed from a semi-liquid secretion, which is produced in the 

 internal organs, is forced through minute apertures at the will of 

 the animal, and hardens into a thread as soon as it comes in con- 

 tact with the air. 



Here, however, the resemblance ceases. The threads of the 

 caterpillar are double, or rather are composed of two lines fused 

 together throughout their length, the two half lines proceeding 

 from a large silk-secreting tube at either side of the body, and 

 uniting at the mouth, where they become fused together by pass- 

 ing through a short tube common to both. The threads of the 

 spider are much more complex, each being formed of a vast 

 number of smaller lines, which are produced from a peculiar or- 

 gan termed the " spinneret," which is placed at the extremity of 

 the body. In consequence of its position, the spider always 

 hangs with its head downward while lowering itself by means of 

 its line. 



The spinnerets are externally like little rounded projections, 

 arranged in pairs, and four, six, or eight in number. They are 

 variable in shape, mostly being rounded, but sometimes being so 

 long that they have been mistaken for feelers. The spinnerets 

 are covered with a multitude of very minute hair-like append- 

 ages, which are, in fact, the tubes through which the liquid secre- 

 tion is forced into the air. All the threads which proceed from 

 these tubes are joined into a single line ; and it will be at once 

 seen that very great strength is obtained by making the line com- 

 pound instead of single. 



The best known of these creatures is the common Gaeden 

 Spider {Epeira diadema), sometimes called the Geometric Spi- 

 der, whose beautifully radiated net is so familiar that its general 

 shape requires no description. Suffice it to say that the spider 

 exhibits wonderful skill in placing its web, making a frame-work 

 of very strong threads or ropes, and then spinning the net itself 

 between them. Very great elasticity is thus obtained, for the 

 threads are exceedingly elastic ; so that, although stretched toler- 

 ably tightly, they will yield to pressure, and immediately recover 

 themselves. This property is very needful, in order to enable 

 them to resist the wind, to which they are so fully exposed. 



