SPIDERS 149 



the much maligned, long-legged house spiders {Tegenaria spp.) 

 which spin cobwebs in the corners of rooms and outhouses; and 

 the garden spiders (Araneus spp.) whose dew-spangled orb webs 

 glistening in the sunlight lend their beauty to the autumn morning. 

 All spiders spin silk, but by no means all of them live sedentary 

 lives in webs: if they did, a large amount of potential food in the 

 form of insects would not be exploited. In fact the more primitive 

 species tend to use silk only for building their retreats and for 

 weaving the cocoons in which they lay their eggs. Indeed, it has 

 been suggested that predation by primitive hunting spiders upon 

 early wingless insects may have been one of the main factors that 

 engendered the evolution of insect wings. When their prey took to 

 the air to escape, spiders evolved aerial webs as a means of trapping 

 it in flight. 



The Araneae or spiders resemble the whip-scorpions in having 

 the cephalothorax (prosoma) and abdomen (opisthosoma) separ- 

 ated by a waist formed by the constriction of the pregenital somite; 

 in having the abdomen in primitive forms composed of eleven seg- 

 ments, in the presence of two pairs of lung-books opening behind 

 the sternites of the first and second abdominal segments; and in 

 having median and lateral eyes in the carapace. They differ from 

 them in that the appendages of the third and fourth abdominal 

 somites have been retained as the so-called spinning mammillae 

 for the manipulation of silk secreted by complicated glands in the 

 abdomen; in the presence of a poison gland in the mandibles or 

 chelicerae, the second segment of which forms a sharp, piercing 

 fang with a single orifice at the tip for the exit of the poison; in the 

 simple leg-like non-prehensile palpi; and the conversion of the 

 terminal segment of the palp of the male into a sperm-carrier. 



Although the order is a homogeneous one, the phylogenetic and 

 systematic problems involved in distinguishing the various families 

 are often complex and several different classificatory schemes have 

 been proposed (e.g. Bristowe, 1938; Petrunkevitch, 1933, 1939, 

 etc.). Three sub-orders are now generally recognised. The first, 

 Liphistiomorpha, is characterised by the fact that the abdomen 

 has retained its primitive segmentation, being provided with eleven 

 tergal plates and other atavistic qualities. The spiders of this sub- 

 order belonging to the family Liphistiidae, of which the best 



