3190 THE JOINTED ANIMALS 



the various kinds of nets became evolved. Another use to which the spinning of 

 threads may be put is that of flying. This is especially practiced by young spiders, 

 who on fine autumnal days climb to the tops of bushes and fences, and, raising the 

 abdomen into the air, emit a thread or tuft of threads which blowing away in the 

 wind soon become large and strong enough to carry the spider, sometimes to great 

 heights above the ground. It was originally supposed that these threads were spun 

 by a species called the gossamer spider, but it is now known that the habit is 

 practiced by young spiders of different families. Floating about in the air, these 

 fine threads meet and, becoming entangled, form masses of web, which ultimately 

 fall upon the bushes and fields, sometimes covering them thickly with a white coat- 

 ing of fine silk. 



SEGMENTED GROUP SUBORDER Mesothelae 



Spiders may be divided into the two main groups, Mesothelce and Opisthothela . 

 In the former, the spinning mammillae, eight in number, are situated in a cluster in 

 the middle of the lower surface of the abdomen; the upper surface of the latter 

 being covered with a -series of nine dorsal plates, resembling those of scorpions, 

 while its lower surface is similarly furnished with two sternal plates covering the first 

 and second pairs of lung sacs. In these characteristics the group differs from other 

 spiders, and in having the abdomen segmented it constitutes a kind of link between 

 them and the tailless Pedipalpi. It likewise resembles the latter in the structure 

 and situation of the breathing organs, and also in the mode in which the mandibles 

 are articulated to the cephalothorax; their basal segments being directed forward, 

 parallel to each other and the long axis of the body, while the second segments or 

 fangs are directed backward, also nearly parallel to the longitudinal axis. The 

 eight eyes are situated on a tubercle close to the front edge of the flat and broad 

 carapace; the median being small, and the lateral larger and placed in a semicircle 

 on each side. The long and powerful legs are armed with spines, and tipped with 

 three claws; their coxae being long, whereas those of the palpi have no long 

 maxillary process as in most other spiders. This group comprises only the family 

 Liphistiidce, with the genus Liphistius, of which there is one species from Penang, 

 and another from Sumatra; both of large size, measuring about two inches in length. 

 Nothing is known of their habits. 



TYPICAL GROUP SUBORDER Opisthothelae 



In this group the abdomen is not segmented, and the spinning mammillae of 

 which there are never more than six, owing to the disappearance or fusion of the 

 inner branches of the first pair of appendages have moved to the hinder extremity 

 of the abdomen. It is separable into the sections Mygalomorphce and Arach- 

 nomorpha. The former group includes the forms making the nearest approach to 

 the preceding suborder. The spinning mammillae are reduced in number, being 

 usually only four, owing to the disappearance of the anterior pair of appendages, 



