155 



The Araneae are divisible into two groups, which may be tabu- 

 lated as follows : 



a. Abdomen furnished v,-ith 9 distinct terga like 



those of the Amblypygi ; spinning-mamillse 

 8 in number, and situated in the middle 

 of the lower surface of the abdomen MESOTHEL^E. 



b. Abdomen without terga ; spmning-mamillse 



never more than 6, and situated at the 



posterior end of the abdomen OPISTHOTHEL^E. 



Fig. 52. 



A. Cephalothorax and abdomen of Liphistius, to show structure of the Mesothelae, 



B. Ditto of one of the Mygalomorphse, to show structure of this group. 



C. Ditto of one of the Arachnomorphae, to show structure of this group. 



a, thoracic fovea ; b, ocular area; c, basal segment of mandible; d, fang of 

 mandible; e, coxae of palpus and legs; /, pedicel; g, 1st tergal plate of 

 abdomen ; k, anal papilla ; i, external, k, internal branch of posterior spinning- 

 organ in A, and anterior and posterior spinner in B and ; I, posterior, and 

 m, anterior breathing-organ. 



MESOTHEL^E. 



Abdomen segmented, its dorsal surface furnished with distinct 

 terga, its ventral surface with two distinct sterna in front, the 

 anterior covering the generative aperture and the pulmonary 

 organs of the 1st pair, the 2nd covering the pulmonary organs of 

 the 2nd pair. Spinning-mamillfe 8 in number, 4 external seg- 

 mented and 4 internal unsegmented, forming a cluster in the 

 middle of the lower surface of the abdomen immediately behind 

 the second sternum. 



The Mesothelae are represented at the present day by a single 

 family and genus. 



