602 USES OF SPIDERS' WEBS. 



spinnerets, as they are called, are two in number, but in the spider they are almost innumer- 

 able, so that the apparently single thread of the tiniest spider, minute as it may seem, and 

 really is in fact, is composed of many hundred finer threads all collected into one strand, like 

 the fibres of hemp in a rope. The strength obtained by this form of structure is very great, 

 and the line is not only strong, but elastic, capable of being drawn out like an India-rubber 

 thread and resuming its original length when the extending force is removed. 



As regarding the gossamer web, Mr. Blackwall makes the following observations : 

 "Although spiders are not provided with wings, and consequently are incapable of flying, in 

 the strict sense of the word, yet, by the aid of their silken filaments, numerous species, belong- 

 ing to various genera, are enabled to accomplish distant journeys through the atmosphere. 

 These aerial excursions, which appear to result from an instinctive desire to migrate, are 

 undertaken when the weather is bright and serene, particularly in autumn, both by adult and 

 immature individuals, and are effected in the following manner. 



" After climbing to the summits of different objects, they raise themselves still higher by 

 straightening the limbs ; then, elevating the abdomen, by bringing it from the usual horizontal 

 position into one almost perpendicular, they emit from their spinners a small quantity of viscid 

 fluid, which is drawn out into fine lines by the ascending current occasioned by the rarefaction 

 of the air contiguous to the heated ground. Against these lines the current of rarefied air 

 impinges, till the animals, feeling themselves acted upon with sufficient force, quit their hold 

 of the objects on which they stand, and mount aloft. 



"The webs named gossamer are composed of lines spun by spiders, which, on being 

 brought into contact by the mechanical action of gentle airs, adhere together till, by continual 

 additions, they are accumulated into irregular white flakes and masses of considerable magni- 

 tude. Occasionally, spiders may be found on gossamer webs after an ascending current of 

 rarefied air has separated them from the objects to which they were attached, and has 

 raised them into the atmosphere ; but as they never make use of them intentionally in the 

 performance of their aeronautic expeditions, it must always be regarded as a fortuitous circum- 

 stance." 



The same writer also remarks that the various directions in which these gossamers are 

 known to sail is in no way attributable to the will of the spider, but merely to the currents of 

 air through which the webs float. He also reviews the opposite opinions regarding the pro- 

 duction of the first lines of the web. Some writers say that the spider has the power of 

 projecting its threads in any direction which it may choose, while others assert that it has no 

 such power, and that the creature is forced to wait for a current of air which can bear the 

 slender thread on its breath. After noticing the arguments and experiments on both sides of 

 the question, he comes to the conclusion that the spider is indebted to the air and not to its 

 own projectile capabilities. 



Strong and elastic as these webs may. be, they have never yet been put to any useful 

 purpose, save to check the bleeding of a cut finger, or to form the cross- wires of an astronomer's 

 telescope. The thread of many species is suitable enough for manufacture, but it cannot be 

 supplied in sufficient quantities. Spiders cannot be kept in any number, as they would be 

 always fighting and eating each other ; and they are so voracious that they could not be prop- 

 erly furnished with food, flies being difficult to catch in many parts of the year, and in the 

 cold months quite unattainable. As a proof that if the web could only be obtained in suffi- 

 cient quantity it might be woven into various articles of apparel, there are now in existence 

 several pairs of gloves, stockings, and other fabrics that have been made, though with very 

 great difficulty, from this substance. 



The odd-looking spider called ArJcys lander is seen at Fig. E. It is a native of Brazil 

 and the surrounding countries. The cephalo-thorax of the spider is orange-yellow, with a line 

 drawn transversely over it, and changing to a brilliant red at the point on each side. The 

 round spots on the abdomen are bright yellow ; the hinder feet are covered only with short 

 do-.vn, but those in front are furnished with strong spines. 



At Figs. B and D are represented the two sexes of Thomisits citreus, for the purpose of 

 shewing the great difference in their dimensions and general shape, the female being twice as 



