COMPAKATIVE JIOEPHOLOGY OF THE GALEODID.^. 349 



(3) The Pi'otntsible Organ at the T'q)s of the Pedifalps. — The invagination at the tips of 

 the pedipalps, the sensory nature of Avhich is evident directly its structure is taken into 

 account, requires to he described in detail. 



The chitinous mechanism is as follows : — A pair of soft-skinned lips (PI. XXXI. 

 fig. 10) open transversely across the tip of the limb. The ventral lip has no hard 

 framework, but the dorsal is only soft where it is in contact with the ventral ; it soon 

 becomes a solid chitinous arch or lid, which moves on hinges at its ends (fig. 11). This 

 lid is opened by a muscle in the next proximal joint (tig. 12, m^\ a long tendon from 

 the muscle being attached to the lid on that side of the line passing through the hinges 

 which is opposite to that on which the lips occur. The aperture leads into a deep conical 

 invagination, running through the whole length of the joint, which is free in Galeodes 

 (PI, XXIX. fig. 3, and PI. XXXI. fig. 12), but fused with the next proximal joint 

 in Rhax (PI. XXIX. fig. 4). The folded walls of the invagination gradually converge, 

 and run down the tibia as a long tendon. This tendon is attached to a very powerful 

 muscle (Wo)' which almost fills up the proximal end of the tibia. The contraction of this 

 muscle draws down the invagination and tightly closes the lips. 



The whole of this chitinous invagination is covered by an epithelium continued down 

 the tendon as far as the muscle, where it becomes lost to sight. The green pigment- 

 cells {cf. p. 331) gravitate towards the tendon as towards the outer cuticle. 



The epithelium covering the inner ventral face of the flattened conical invagination is 

 deep, contains several layers of smaU nuclei (Pi. XXXI. figs. 13, 13 a), and is sensory. 

 The sensory cells send fine hair-like processes through the cuticle, which project into 

 the invagination, clothing its ventral wall like a fine velvet. These hairs are about 

 1 n thick and 75 ^i long ; the sm-face formed by their tips is wavy, perhaps for the 

 purpose of increase (PI. XXXI. figs. 13 and 14). 



The cuticle, traversed by these hair-like processes, is regularly channelled through by 

 rows of pores close together, so that it has, at times, a net- or lattice-like appearance. It 

 is considerably thickened, perhaps to keep the sensory area spread out. It is, neverthe- 

 less, liable to be folded longitudinally, the longitudinal bars of the latticework being 

 thicker than the transverse (fig. 14). The dorsal sm"face of this sensory invagination is 

 entirely free from such hairs, and is extremely thin and delicate. When the lips are 

 closed the tips of the sensory hairs rest against this membrane. 



When the Ups are open the up2)ermost sensory haii-s jn-oject through the gape. They 

 :are not, however, confined to this part, but continue right down to near the extreme 

 base of the pit, where it runs into the tendon {cf. fig. 12). Pigs. 15, 16, 17 show the 

 organ fully protruded, this protrusion probably being effected by blood-pressure *. In 

 this condition the sensory haii-s deej) down in the base of the invagination are brought 

 into closer contact with the outer air. 



As to the function of these organs there has been some difference of opinion. In 



* lu its evagioated condition the outer skin is very smooth and glistens like satin, wliich fact would account for 

 the following description of an eye-witness : — '• When the palpi arc applied to any object, a sort of phosphorescent 

 flame seems to be emittted from them." — Murray's ' Economic Entomology,' p. 42. 



