558 CLASS ix. 



The feet or legs of arachnids do not present exactly the same 

 typus as those of insects. They consist usually of seven joints, and 

 are not thinner towards the extremity, so that the tarsi differ less 

 from the other parts than in insects. If we suppose that the two 

 last joints belong to the tarsus, then the tibia consists of two joints 

 of which the first in some is the longest (e.g. Scorpio and Phrynus), 

 in others the second. The long joint that precedes it is the femur 

 which succeeds a short, inversely conical joint corresponding to the 

 trochanter in hexapod insects. The first joint, broader, commonly 

 inversely conical, by which the feet are attached to the cephalo- 

 thorax, corresponds to the hip (coxa) of insects. In Plirynm, the 

 tarsus of the fore legs consists of a great number of joints (thirty 

 and more), of extraordinary fineness, and in the remaining feet of 

 three joints. The last joint of the tarsus has usually two curved 

 booklets, and in some a membranous or vesicular cushion (pulmllus) 

 in addition at the under side. What is most distinctive in the com- 

 position of the feet in arachnids, is the division of the tibia into 

 two pieces. In Phrynus, the tibia of the fore-feet, like the tarsus, 

 consists of numerous thin joints ; those of the second and third pairs 

 of feet of the usual number, two ; those of the fourth pair of five, of 

 which the first exceeds the rest in length remarkably. 



The cephalothorax often presents a line or groove on each side 

 of the simple eyes placed in the middle, indicating an imperfect 

 separation, so that the head looks like a wedge or triangle, with the 

 point turned backwards, upon the thorax. The upper surface of 



Sc. not. 2e SeVie, I. Zoolog. p. 7, and by ERICHSON, Entomogr. s. 8.] In the scorpions 

 there are two horny triangular plates between the first pair of feet, which may be 

 regarded as mentum, a part wanting in the rest of the anachnids. An upper lip 

 (labrum) is not present in these any more than in the rest. According to this view 

 arachnids would have only three pairs of feet, like most insects. Yet Zoology must 

 nevertheless still continue to assert that arachnids have four pairs of feet, since, in 

 reality, four pairs of jointed appendages of the cephalothorax do always act as feet. 

 Even the jaws of hexapod insects are in a wider sense modified feet. Feet and jaws 

 are parts having the same fundamental form. This is proved by the history of develop- 

 ment. Both these parts are, according to the investigation of KATHKE in the Cray-fish, 

 of the same form, and the dissimilarity between feet and jaws, which is seen in perfect 

 cray-fishes, is merely the consequence of subsequent development (Untersuchungen tiler 

 die Bildung u. EntwicTcelung des Flusskrebses, Leipsig, 1829, fol. s. 67, 68). In young 

 and still imperfect individuals of Cyclops quadricornis, according to the figures of 

 JURINE, the upper jaws and the last pair of under jaws serve for swimming, and have 

 much resemblance to the feet which are developed only at a later period. RATHKE loc. 

 cit. p. 73. 



