334 ARACHNOIDEA AND PAL&OSTRACA. 



joint of the palps. The ova are usually surrounded by 

 silken cocoons, which are carried about by the mother or 

 carefully hidden in nooks or nests. 



Spinning. Compression of the spinning glands causes a flow of liquid 

 silk through the fine spools of the spinnerets. The extremely thin fila- 

 ments 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 com- 

 pound 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 

 on the hind legs a special comb of stiff hairs. 



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 intersecting 

 in one centre. Secondly, 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. Thirdly, 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 

 entire fabric is marvellously sensitive, for 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 tip-toe 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. 



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

 It is calculated that the disproportion is sometimes such as would be 

 observed if a man 6 feet high and 150 pounds in weight were to marry 

 a giantess of 75-90 feet high, 200,000 pounds in weight. It may be 

 that the smallness of the males is mainly due to the fact that they are 

 males ; others explain it by saying that the smaller the males are, the 

 less likely they are to be caught by their frequently ferocious mates. 

 It is difficult, however, to understand how this characteristic smallness, 

 though perhaps advantageous and likely to be favoured by natural 

 selection, can be entailed on the male offspring only. But this difficulty 

 in regard to inheritance is one which besets many similar interpretations. 



The males are often more brilliantly coloured than the females, per- 

 haps, again, because they are males, though what the physiological 



