350 ME. H. M. BEENA.ED ON THE 



describing the sbavp sense of smell of these animals, Lichtenstein and Herbst (48, p. 52) 

 state that it is eliiefly localized in the hollow knob at the tip of the feeler. Dufour, 

 however, who discovered the retractile organ itself, interpreted it as being a sucker. 

 Koch had adopted the earlier view, which, from the above description, seems almost 

 certainly the correct one. That it is not an organ " pour s'accrocher ou grimper " 

 (Dufour, and recently re-stated by Bertkau, 20, and Gaubert, 32) follows from the fact 

 that it has no teeth and no circular or radial muscles, and is lined with fine hairs on. 

 only one side, which hairs extend right down into its base, where they could take no 

 part in any external action. Turther, Avhen fully distended (PI. XXXI. figs. 15, 16, 17) 

 it does not make a complete circle as a sucker must do, and is not conveniently placed, 

 opening not downward but outward. All the observations on living animals show 

 that the pedipalps are organs of fine sensation *. 



So far as is at present known, the only other Arachnids with invaginations at the tips of the pedipalps 

 are the male Spiders. In these they are specialized as sexual organs ; the transition between a 

 sensory invagination and a spermatophore carrier is not difficult to imagine when we remember that 

 the Spiders have lost the highly sensory organs which, presumably, were at one time present on the 

 limbs, either in front of or behind the genital aperture (compare the pectines of Scorpio and the 

 racquets of Galeodes). 



In other Arachnids there is no doubt that the pedipalps, as occupying the foremost position of all the 

 limbs, are the seat of fine sensation. The Scorpions and Pseudoscorpions use their pincers with great 

 caution, as if feeling with them. Hansen has described and figured fine tactile hairs on the pincers of 

 Scorpio. Long delicate hairs a])pear to rise from the bottom of cup-like pits on the pincers of some 

 Pseudoscorpions. In Phrynus, within the most distal joint or claw of the pedipalps, there is a sensory 

 area surrounded by hairs of different shapes |. 



(4) The Racquet-organs. — Five of these, as is well known, are found, in most, if not in 

 all, genera, on each of the last walking-legs, two on the coxa, two on the trochanter, 

 and one on the femur. 



On comparing this with the pectines of Scorpio we find a striking parallel, inasmuch as the pectines 

 in many genera show clearly that they consist of the same thiee joints, i. e. of the coxa, the trochanter, 

 and a small portion of the femur of a pair of legs behind the genital aperture. We may perhaps 

 conclude from this that, in the original Arachnid, the limbs both in front of and behind the aperture 

 were provided with sensory organs on these joints. 



The racquet-organs stand sti-aight out ventrally from the cuticle of the leg as tubular 

 outgrowths, slightly folded round their bases for the sake of flexibility. This tubular 

 shaft varies greatly in length, being long in Galeodes, which runs high off the ground 

 on its long and jiowertul legs, but very short in Rhax, wliich has comparatively short 



* " Les palpes s'agitent alors commc pour interrogcr I'espace " (Dufour). See, further, the account in Murray's- 

 ' Economic Eutomology,' quoted in the preceding note. 



t In the Ann. & Mag. N. H. ser. 6, vol. xi. 1S93, I stated that this area sloped away sideways under the 

 cuticle into a pocket which ran down into the next joint, and was provided, as in (laleodcs, with sensory hairs. 

 I have been unable to find any trace of this pocket in sections, and have re-examined the cleared specimen in which 

 it seemed so apparent. It was some time before I found the clue to the discrepancy ; the cleared specimen is 

 apparently preparing to shed its skin, and the sensory area is repeated beneath the cuticle and reaches into the 

 next joint, thereby giving the appearance which deceived me. 



