COMPAEATIVE MOEPHOLOGT OF THE GALEODID.-E. 327 



Scorpions and the PscudoscorpionSj in which the pedipalps are seizing organs, the 1st pair of legs have 

 retained their original loconiotory functions unmodified. The comparatively slow, deliberate manner 

 of hunting prey may account for the fact that they require no more specialized feelers than the 

 pedipalps themselves, which are, as everyone who watches them alive knows, highly sensitive. 



The Remaining Liinhs. — The i-emaining three pairs of legs are long and powerful, the 

 last two having the femur divided by an extra joint, as Gaubert (32) has pointed out, 

 hut whether the reasons he has given for this are correct I am unable to judge, having 

 never seen the animals alive. The last of the three pairs of legs carries the remarkable 

 racquet-shaped sensory processes which will he described in detail in the section on the 

 sensory organs. 



General Eemarks on the Cephalothoracic Appendages. — These six pairs of limbs are the appendages of 

 the first six segments, i. e. of that region of the Araehnidan body which is specialized for locotnotory, 

 sensory, and predatory functions, while the region immediately following is typically developed into 

 a nutritive and generative sac, and, as such, loses its limbs. These six pairs of limbs are characteristic 

 of all adult Arachnids, although the possession of six pairs of appendages on a specialized anterior 

 region of the body would not constitute an animal an Arachnid. The arrangement of these limbs, 

 and especially of those nearest the mouth, supplies the most important diagnosis of the class. In 

 no case does the first pair of limbs form feelers; in no case [? certain specialized Acaridse] do the 

 limbs form biting jaws projecting into, or arranged close to, a mouth-aperture. In all cases, the first 

 pair of limbs are jointed, seizing and crushing limbs, transposed from behind to a position in front of 

 and above the mouth, which is typically a beak. Special feelers are sometimes dispensed with, at other 

 times developed out of the 2ud, at others out of the 3rd, at others, again, out of the 2nd and 3rd pairs 

 of limbs; while, in most cases, the 2nd pair of limbs assists the 1st in the capture and crushing of prey, 

 the juices of which alone are sucked in by a mouth which is typically provided with a straining apparatus. 



These characters constitute the Arachnids a class removed entirely from all other Arthropods, in 

 which, typically, the first pair of limbs are sensory feelers, while a certain number of those which follow 

 form true jaws, not only to crush food but to push it into the mouth, round which they are ranged. 



Certain Acari, in which the mouth-limbs (perhaps fusing with a primitive beak) form a piercing 

 sucking apparatus, distantly approach, hy secondary specialization, those Arthropods of other groups 

 (Crustacea and Hexapoda) whose mandibles and maxillae are also secondarily specialized into a sucking 

 proboscis. 



These six pairs of cephalothoracic appendages, constant in the (adult) Arachnida, show certain 

 interesting variations in their arrangement on the body. These can be gathered at a glance from the 

 diagrams (PI. XXVII. figs. 15-18 and Pl.XXVlII. figs. 1, 2). None of the arrangements can be con- 

 sidered primitive. That represented by certain Acari and Arancffi, inasmuch as the sterna are preserved 

 and the limbs regularly arranged, must be considered as nearest to the original. The circular arrange- 

 ment in the Spiders is certainly secondary. The regular arrangement of the legs in two straight 

 series in Galeodes is primitive, but the disappearance of the sterna is a secondary specialization. 



Another point of interest is the fixation of the coxa; which occurs to some extent in most Arachnids. 

 In Galeodes all are fixed, as is also the case in Thehjphonus and the Phalangidae. In Scorpio the coxae 

 of the first pair of legs are alone movable, those of the other three are fixed. In the Spiders, 

 Phrynidse, and (?) some Pseudoscorpions all are movable *. 



* In fig. 2 (PI. XXVIII.) the coxk certainly appear to be fixed ; hut there is great variation in the arrangements 

 of the coxai in this order. 



