WEB-SPIDERS. 



227 



Instead of making a trap-door nest, this spider spins a long silk tube, closed at 

 the ends, one half of which is buried in the earth, while the other lies loosely 

 among the grass or stones on the surface of the ground. When a fly or beetle 

 alights on this part of the web, the spider slowly and cautiously climbs to the 

 spot, and, invisible all the time to the insect, suddenly seizes it from within, and 

 tearing away the web drags its prey through the aperture, which is then 

 repaired. 



The next section is that of the Arachnomorphcv, which includes the common 

 house and field spiders, and differs from the last in having the basal segment of 

 the mandible vertical instead of horizontal, and the fang closing inwards and 

 backwards. There are generally six spinning mammillae, comprising an anterior 

 two-jointed pair, a similar posterior pair, and an intermediate single-jointed pair. 

 Between those of the front pair there is either a functionless membranous piece, 

 the colulus, or a paired plate, the cribellum, which is studded with the apertures of 

 spinning glands. The eyes are occasionally arranged in three clusters, two being 

 in the middle and three close together on each side ; but usually the three lateral 



field-spiders (Segestria senoculata). a, Female ; b, Male ; c, Arrangement of eyes (enlarged), 



ones are scattered, and the eight eyes placed on the front of the head in two rows. 

 The Arachnomorphce are divided according to their structural characteristics and 

 web-making instincts into a number of tribes each containing one or more families. 

 The first tribe, Umbellitelarice, contains the single family Hypochilidce, represented 

 by the genus Hypochilus in North America and Ectatosticta in China. These two 

 spiders differ from all the rest in having the hinder pair of breathing-organs in 

 the form of lung-sacs; the cribellum and calamistrum being present and the 

 long and slender legs furnished with three claws. In the genus Hypochilas, 

 which is found in the forests of Tennessee, the web is constructed beneath over- 

 hanging rocks and cliffs and has somewhat the form of an inverted saucer, made 

 of thick white silk and kept in place by a loose network of threads. Beneath this 

 web the spider remains upside down, and it has the habit, common to other species, 

 of violently shaking the web when alarmed. In the tribe Pseudoterritelarice, 

 as in the rest of the section, the breathing-organs of the hinder pair are in the 

 form of tubular trachea?, but their apertures are widely separated and situated 

 immediately behind those of the front pair. There is no cribellum nor 

 calamistrum, and the eyes are reduced in number, being usually six, but some- 

 times, as in Hops, only two. Two well-known European representatives of this 

 tribe constitute the genera Dysdera and Segestria. The former, found not 



