1902.] ANATOMY OF THE PEDIPALPI. 175 



The entrance to the alimentary canal between the camarostome 

 above and the coxse below is a wide, ti'ansversely crescentic slit with 

 the concavity looking upwards. Its floor and outer sides are formed 

 by a thickly chitinized, deeply hollowed plate, continuous along 

 its upper and exterior edge on each side with the adjacent area 

 of the inner surface of the coxa, of which it is a part ; and 

 postei'iorly with the posterior extremity of the side of the cama- 

 rostome, to which it is attached by membrane. It is finely 

 grooved transversely, and beset with a thick coating of short 

 delicate hairs. Posteriorly it is constricted, and in the middle 

 line passes into the relatively narrow pharyngeal portion of the 

 alimentary canal (text-figs. 42, 0, lam., p. 177, and 44, lam.,^. 183). 



The roof and inner walls of the crescentic slit are formed by 

 the sides and lower surface of the camarostome, which lies in the 

 hollow of the plate described above, the two being united by 

 membrane only along their posterior edges. Fine hairs clothe 

 these surfaces of the camarostome, and a thick fringe of hairs 

 projects beyond the apex from near the distal extremity of this 

 organ. The under surface of the camarostome is posteriorly 

 continuous in the middle line with the dorsal wall of the pharynx, 

 as already stated (text-fig. 41, A, cam., ph., p. 173). 



The crescentic slit above described is not closed above, but 

 opens on each side between the outer surfaces of the camarostome 

 and the adjacent inner surfaces of the coxse of the chelae, which 

 are continuous with the horny j)late forming the outer sides and 

 floor of the slit. Fluid taken into the slit would be prevented 

 from escaping upwards through its open extremities by the hairs 

 clothing the inner side of the coxfe (text-figs. 41 & 42, mh., pp. 173^ 

 177) and the outer portion of the upper surface of the camarostome, 



It will thus be clear that the so-called mouth of the Thely- 

 phonidfe, i. e., the aperture that lies between the tip of the 

 camarostome above and that of the horny plate below, is a 

 secondarily acquired aperture produced by the forward extension 

 and union of the coxae of the chelje and the elongation and 

 depression of the camarostome. The true mouth, i. e., the entrance 

 to the stomodseum or foregut, representing the mouth of the 

 Scorpions and Phrynus, is the relatively narrow aperture by 

 which the pharynx debouches into the above described slit (text- 

 fig. 41, A, m., 2)h., p. 173). 



The key to the mode of formation of this ai-rangement is to be 

 found in the mouth-parts of the Amblypygi [Phrynus), which so 

 far, at all events, as the freedom of the coxae of the chelae is con- 

 cerned, are admittedly less specialized than those of Thelyphonus. 

 In Phrynus the camarostome is relatively a very small fiexible lobe 

 overhanging the mouth, and furnished dorsally with a small heart- 

 shaped sclerite representing the chitinous plate of Thelyphonus 

 (text-fig. 42, A, B, cam., m., p. 177). The coxae of the chelae have 

 fused below the mouth and separate it entirely fi'om the forwardly 

 directed prosternal plate of the prosoma, which is the sternum of the 

 second postoral somite (text-fig. 42, A, B, s^., p. 1 77). When forcibly 



