22 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. IIQ 



ently developed, and unrelated to the mouth cone of the Palpigradi. 



If the mouth structure of the Palpigradi really is primitive for the 

 arachnids, then there can be no direct relationship of the Arachnida 

 to the Xiphosurida, and the coxal lobes of the higher arachnids must 

 have been developed quite independently of those of the xiphosurids. 



The mouth of Prokoencyiia zvheelcri, Rucker (1901) says, "leads 

 into a strongly-chitinized pharynx (fig. 6 C, Phy). This in turn runs 

 into a very delicate oesophagus (Oe) which penetrates the cephalo- 

 thoracic nerve mass, only to dilate immediately into a pouch-like 

 sucking stomach" (Pvent). The pharynx is shown in one of Rucker's 

 figures to have dilator muscles arising dorsally on the upper wall of 

 the mouth cone, and ventrally on the lower wall. According to Borner 

 (1902), the walls of the pharynx contain a dorsal plate, which is the 

 under surface of the labrum, and a ventral plate, which is the upper 

 surface of the suboral prosternum. The "pharynx" of the Palpigradi 

 would thus appear to be a specialized preoral cavity ; yet Kastner 

 (1932b) ascribes it to the stomodaeum (Vorder-Darm). 



III. THE SOLPUGIDA 



Most conspicuous of the feeding organs of the solpugids are the 

 huge, two-segmented chelicerae (fig. 7C), directed straight forward 

 from the anterior section of the body (A), which latter appears to 

 be constructed particularly for their support, though it carries also 

 the pedipalps and the first pair of legs. The solpugids are said to 

 employ principally the last three pairs of legs for locomotion, the 

 first legs being often used as accessories to the palps for catching and 

 holding the prey. The coxae of the pedipalps and those of the first 

 legs are firmly united on each side (B, IICx, IIICx), and the two 

 pairs are supported on a single T-shaped sternal plate, which would 

 appear to represent the deutosternum and the tritosternum combined. 

 The narrow, deeply channeled anterior part of the plate {IIS) lies 

 between the pedipalp coxae; the posterior part is a transverse bar 

 {HIS) behind the first leg coxae. The following three sterna are 

 individual plates, though each is divided by a median groove that 

 forms an internal ridge. That these plates are sterna and not the coxae 

 of the legs is shown by the presence of large apodemal structures 

 arising from them, and by the fact that the legs have a full comple- 

 ment of segments, including two trochanters. 



The pedipalps arise entirely behind the mouth region (fig. 7B), 

 as they do in the Palpigradi, but in the solpugids their large coxae 

 diverge forward beneath the chelicerae (B), and each is produced 



