Mr. A. Tulk on the Anatomy 0/ Phalangium Opilio. 159 



(PI. III. fig. 9. y) is formed by a division of the joint into two 

 portions : the internal (PI. III. fig. 9. v), more or less convex, has 

 its margins raised in front into ridges, which circumscribe a 

 quadrilateral surface, and abuts against the anterior part of the 

 epipharynx, and terminates by bending upon itself in an outward 

 direction, to form, behind the second joint of the palpus, a trans- 

 verse oval projection of a white colour, and beset with bristles 

 (PL III. figs. 9 and 10. tt) ; while the external is continued as an 

 elongate and flattened piece (Pi. III. fig. 10. 0), concave within, 

 and with thickened edges, to be connected with a corneous arci- 

 form fold of the maxillae (n), presently to be^ described. That 

 the above pieces are in reality but a pair of coxal joints, modified 

 like those of the foot-jaws of the Crustaceans, or their corre- 

 sponding parts in the other Arachnida, to subserve a double 

 function, is evident both from their position and general form ; 

 and in species where the palpi are largely developed, as P. Cor- 

 nutum, this analogy becomes still more striking. I shall there- 

 fore consider these as the true basal joints of the palpi, each of 

 which will thus consist of siw principal divisions, comparable to 

 those of the legs, instead of five, as described by authors. The 

 second joint of the palpus (PL III. fig. 3. 2), representing then 

 the exinguinal or trochanteric of the extremities, shorter than the 

 one succeeding, is articulated in a ginglymoid manner to the 

 basal. It is broadest superiorly, its upper surface slightly con- 

 cave, its lower convex, and it is dotted over with short stiff bris- 

 tles. The third, fom'th and fifth joints (3, 4, 5) are constructed 

 upon the same plan with the second, the third nearly equalling 

 in length the two others, and curved slightly upwards, with the 

 surface spined and bristly. The fourth and fifth, analogous to 

 the divided tibia, as the former was to the femoral, are more 

 curved than the rest, and dilated anteriorly. The sixth (6), ter- 

 minal or tarsal joint, is the longest and narrowest of all, cylin- 

 drical, and widening gradually towards the apex, where it termi- 

 nates in an obtuse, rounded extremity, supporting a single small 

 hook or unguis, its whole surface being plentifully furnished, like 

 that of the two preceding, with bristles of unequal length. When 

 the palpi are at rest, they are bent upwards at an acute angle 

 with the basal joint, and downwards again, at the junction of the 

 third and fourth articulations, the first of which rests against the 

 outer side of the cheliceraj projecting above the anterior margin 

 of the thoracic shield. 



Hahn (in his 'Die Arachniden') has figured the sexual differ- 

 ences in the palpi of a male and female P. Opilio, The fourth 

 joint of the male is represented as having a haiiy prolongation 

 springing from it, nearly equalling in size the joint itself, while 

 that of the female is destitute of any such appendage, and the 



