SPIDERS. 371 



spiders at birth are often very different in details from their 

 later stages. 



Spinning. Muscular compression of the glands causes a flow of 

 liquid silk through the fine spools of the spinnerets. The extremely 

 thin filaments from each spinneret unite into a thread, and the thread 

 of one spinneret is often combined with that from the others. In this 

 way a compound thread of exquisite fineness, though rivalled by a 

 quartz-fibre, is produced ; but two or four separate threads are often 

 exuded at the same time. Before beginning to "spin," the spider 

 often presses the spinnerets against the surface to which the thread is 

 to adhere, and draws the filaments out by slowly moving away. Often, 

 however, the filaments ooze out quite apart from any attachment. The 

 legs are also much used in extending and guiding the thread, and some 

 spiders have, as has been mentioned, a special comb (calamistrum). 



One of the most important ways in which the secreted threads are 

 used is in forming a web. The common garden spider (Epeira} makes 

 a web which is a beautiful work of unconscious art, and very effective 

 as a snare for insects. The spider first forms "foundation lines" 

 around the selected area ; it then swings across the area with the first 

 " ray," which it fixes firmly ; another and another is formed, all inter- 

 secting in one centre. Thirdly, it starts from the centre, and moves 

 from ray to ray in a long wide spiral gradually outwards, leaving a 

 strong spiral thread as it goes. Fourthly, the spider moves in a closer 

 spiral from the circumference inwards, biting away the former spiral, 

 replacing it by another, which is viscid and adhesive. It is to this that 

 the web chiefly owes its power of catching insects which light there. 

 There is usually a special thread running to the adjacent hole or nest, 

 and the spider feels rather than sees when a victim is caught. 



The spun threads are used in many other ways. They line the nest, 

 and form cocoons for the eggs. They often trail behind the spiders as 

 they creep ; they greatly assist locomotion, and are used in marvellous 

 feats of climbing. Small and young spiders often stand on tiptoe on 

 the top of a fence, secrete a parachute of threads, and allow them- 

 selves to be borne by the wind. The fallen threads are known as 

 gossamer. 



The distribution of spiders, e.g. on islands, does not appear to be much 

 affected by the absence of wings. Many young forms are aeronauts, 

 and many are carried about by the wind apart from ballooning. 



Courtship. The males are often much smaller than the females. 

 The disproportion is sometimes such as would be observed if a man 

 6 ft. high and 150 lb. in weight were to marry a giantess 76-90 

 ft. high, 200,000 lb. in weight. The smallness of the males may be 

 due to the fact that they are males ; others say that the smaller the 

 males are, the less likely they are to be caught by their frequently 

 ferocious mates. 



The males are often more brilliantly coloured than the females. 

 Wallace spoke of the brilliancy of males as due to their greater 

 vitality, and referred the relative plainness of the females to their 

 greater need for protection. Darwin referred the greater decorative- 

 ness of males to the fact that those which varied in this direction found 



25 



