662 



GOSSAMER 



innumerable, 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, 

 belonging 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. 



A. Thdmisus cristutus. 

 E. Arkys lander. 



C. TMmteus Cambridgii. 



B. TMmisus Mreus. (Female.) 

 D. Thdmisus eitreus. (Male.) 



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 alort. 



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 magnitude. 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 



