STUDIES ONT THE ARACHNID MNTOSTKRNITE. 239 



of Galeodes arabs revealed^ liowevei", a joint betweeu the 

 posterior extremities of tlie bars of the V-shaped prosternuni 

 and the diverging pilhirs of the entosternite. 



The question as to wliich of these two arrangements is the 

 more primitive must remain unanswered until tlie origin of 

 the Galeodeau entosternite is settled. If, as Bernard main- 

 tainSj it is nothing but an exoskeletal entapophysis, the con- 

 dition of unbroken continuity with tlie exoskeleton, as 

 manifested in Sol puga, must be regarded as the original, and 

 the jointed condition seen in Galeodes the derivative. If, 

 on the other hand, the entosternite in this order proves to 

 be an entoskeletal element like that of other Arachnids, its 

 fusion with the exoskeleton must be a secondarily acquired 

 chai'acteristic, and its separation therefrom a primitive 

 feature (PI. 14, figs. 26, 27). 



II. The Comparative Mori-hglogy of the Entosternite. 



The evidence favouring the hypothesis that the prosoma of 

 the primitive Arachnid was furnished with a broad segmented 

 sternal area separating the post-oral appendages of the right 

 side from those of the left needs no recapitulation. It may be 

 claimed that the possession of a wide sternal area by the 

 Amblypygous Pedipalpi and all the typical Aranea) is an 

 archaic feature; and that, in this particular at least, these 

 orders are less specialised than the Scorpiones, Solifugse, 

 Pseudo-scorpiones, and Opiliones, where the encroachment of 

 the coxa3 of the appendages, aided in the case of the first 

 and last-named orders by antero-posterior compression accom- 

 panying the forward movement of the generative aperture, 

 has more or less obliterated the sternal sclerites in the middle 

 line. Although modified to a very appreciable extent in 

 the direction of sternal suppression, the prosoma of the 

 Uropygous Pedipalpi is moie primitive than tliat of the 

 four ordera last named, more primitive even than that of 

 the Amblypygi and Araueai in the lesser constriction of its 

 posteriof somite to share in the formation of the waist. 



