326 ME. H. M. BERNARD ON THE 



pair of seizing limbs. Sucli limbs must have powerful bases from which to work. The method in which 

 the bases of the great seizing pedipalps have developed in adaptation to their new requirements varies 

 greatly in different Arachnids. This fact leaves little doubt that the specialization is a secondary one. 



In Schizonotus, the enlarged basal joints of the pedipalps have grown out anteriorly far in front of the 

 chelicerfe. They, however, still lie ventrally to the cephalic lobes — that is, meet in the middle line. In 

 the Pseudoscorpionidffi the arrangement differs from that in Schizonotus, in that the coxal joints of the 

 large pedipalps do not project beyond the front of the body, but posteriorly, thrusting back the four 

 following or ambulatory limbs, which are pushed further from the mouth than in any other Arachnid 

 (PI. XXVIII. fig. 2 does not show this so markedly as it is seen in some genera). In Thehjphonus, the 

 large coxal joints of the pedipalps have found room for development backward, by displacing the 3rd pair 

 of limbs, the coxal joints of which no longer appear on the ventral surface (PI. XXVII. fig. 17). And 

 in Phrynus, the enlarged coxee of the pedipalps have partially displaced the coxie of the 3rd pair of limbs,, 

 though they are still visible from the ventral surface. In both these cases, the comparatively small 

 chelicerae have sunk in between the coxal joints of the pedipalps. But in all these cases the bases of the 

 pedipalps meet ventrally in the middle line. 



In the Scorpions we reach an extreme of specialization. The basal regions of the enormous pedipalps 

 are thrust out anteriorly and laterally. The crowding forward of the walking-legs to the anterior end 

 of the body not only prevents any backward development of the coxae of the pedipalps, but has even 

 forced them apart so that they no longer meet ventrally in the middle line, nor take any part in the 

 formation of the ventral surface of the cephalothorax. 



These changes in the relative development of the chelicerae and the pedipalps have naturally led to 

 great modification in the cephalic lobes, which owe their origin to the translocation of the former. In 

 my preliminary notice of these cephalic lobes, I thought that, as the chelicerae became subordinated to 

 the pedipalps, the cephalic lobes carrying them became wedged in completely between the shoulders of 

 the pedipalps, but that is not the case ; the cephalic lobes still form the whole of the anterior dorsal 

 surface. The relations can be made out by comparing the sections (PL XXVII. figs. 9 a, 9 6, 9 c, and 

 PI. XXVIII. fig. 9). 



Thus, starting with the condition found in Galeodes, the Spiders and Phalaugids, in which the 

 chelicerae are the only true seizing organs, we have every stage in the gradual specialization of the 

 originally simple leg-like pedipalps into complicated seizing and crushing limbs. 



The oi'd Pair of Limbs. 1st Pew- of Legs. — The 3rd pair of limbs, like the pedipalps, 

 are leg-like, but have apparently lost their locomotor functions, and are specialized into 

 a second pair of sensoiy limbs. Like the pedij)alps, they are long in Galeodes, but short 

 in MJuix. In Galeodes, they are also very thin (PL XXIX. fig. 3). The presence of a 

 pair of reduced claws at their tips shows that they were at one time ambulatory legs. 

 Their specialization into feelers in addition to the existing pedipalps must be due to the 

 great activity of these hunting animals *. The special sensory cells at their tips will be 

 described in the section on the sensory organs. No other Arachnid has two pairs of feelers. 



In the Scorpions, Araneae, Pseudoscorpions, and Phalangidae, the 3rd pair of limbs are true ambulatory 

 legs, while in the Phryuidae and Thelyphonidae the tendency shown in Galeodes to become sensory 

 feelers has reached an extreme of specialization. This is doubtless a compensating modification, 

 owing to the secondary transformation of the pedipalps into seizing organs. In these animals, the first 

 pair of legs become long, filiform, many-jointed feelers. It is not immediately apparent why, in the 



* The auimal kingdom presents other examples of a high development of sensory organs with rapidity of motion 

 in the pursuit of prey. 



