MORPHOLOGY OF THE PEDIPALPI. 29 



The two sides run forward, diverging from eacli other, tlie outer 

 side being the longer, and the anterior edge runs obliquely- 

 forward and outward. A thin chitinous cuticle covers both sides of 

 each lamella, between the two layers of which is the blood-space. 

 Occasional cellular columns pass across the blood-space from one 

 cuticle to the other. The cuticle on the dorsal side of each 

 lamella is covered towards the free margin (PI. TV. fig. 9) by a 

 number of vertical chitinous rods, the summits of which are united 

 to form an arcade structure, further away from the free margin 

 these rods become smaller (fig. 10), and seem to be firmly 

 attached to the ventral surface of the overlying lamella. Whether 

 the ordinary small rods are actually continuous with the chitin 

 of the overlying lamella, I cannot be sure, but certain thicker 

 rods which occur here and there certainly are continuous. There 

 is in this region no appearance of an arcade structure. The 

 free edge of each lamella is enormously thickened (fig. 9), the 

 thickened rim tending to run into sharp points on the dorsal 

 surface and along the edge, while it is smoother and more solid 

 on the ventral surface. The arcade structure gradually dies out 

 towards the edge, though it persists for some distance along the 

 thickened portion. 



The posterior side of the air-chamber is bounded by a mem- 

 branous wall, which is strengthened by a network of curved 

 chitinous bars (PI. IV. fig. 11). These bars are every here and there 

 drawn up into blunt processes, and small knobs of chitin make 

 their appearance on the membrane within the meshes. At the 

 sides of the air-chamber where the ends of the free edges of the 

 lamellae are attached to it, the wall is enormously thickened 

 (fig. 12) and drawn out into irregular conical processes. The 

 surface of this part of the wall is further closely covered with 

 stiff hairs. 



The structure of these lamellae differs from that described by 

 Berteaus * for Spiders chiefly in the greatly thickened free 

 margin. In other respects the similarity is very close. 



Caudal Organ. — On the dorsal surface of the last segment lies a 

 pair of oval white spots, which have been called the apertures of 

 the stink-glands (fig. 1, c.o.). Sections through this portion of the 

 integument, however, show that there is no aperture at this point. 

 The chitinous cuticle is much thinner than elsewhere (PI. III. 

 fig. 7), and the underlying layer of cells shows an entirely 

 * La Cellule, vol. v. 



