STRUCTURE AND CLASSIFICATIOK 01' THE ARTHROrODA. 557 



tened foliaceous appendage^ adapted to swimming and respira- 

 tion (trunk limbs of Phyllopods). 



(3) Corm alone developed, with no endites or exites, but 

 provided with terminal chitinous claws (ordinary leg of 

 Peripatus), with terminal jaw teeth (jaw of Peripatus), or 

 with blunt extremity (oral papilla of same) (see fig. 8). 



(4) Three of the rami of the primitive limb (endites 5 and 

 6 and exite 1) specially developed as endopodite, exopodite, 

 and epipodite, the first two often as firm and strongly cliitin- 

 ised, segmented, leg-like structures; the original axis or corm 

 reduced to a basal piece, with or without a distinct gnatho- 

 base (endite 1), typical triramose limb of higher Crustacea. 



(5) One ramus (the endopodite) alone developed — the 

 original axis or corm serving as its basal joint with or 

 without gnathobase. This is the usual uniramose limb 

 found in the various classes of Arthropoda. It varies as 

 to the presence or absence of the jaw process and as to the 

 stoutness of the segments of the ramus, their number (fre- 

 quently six, plus the basal corm), and the modification of the 

 free end. This may be filiform, or brush-like, or lamellate 

 when it is an antenna or palp ; a simple spike (walking leg 

 of Crustacea, of other aquatic forms, and of Chilopods and 

 Diplopods) ; the terminal joint flattened (swimming leg of 

 Crustacea and Gigantostraca) ; the terminal joint provided 

 with two or with three recurved claws (walking leg of many 

 terrestrial forms — e.g. Hexapoda and Arachnida) ; the 

 penultimate joint with a process equal in length to the 

 lust joint, so as to form a nipping organ (chelce of Crusta- 

 ceans and Arachnids) ; the last joint reflected and movable 

 on the penultimate, as the blade of a clasp-knife on its 

 handle (the retrovert, toothed so as to act as a biting jaw 

 in the Hexapod Mantis, the Crustacean tSquilla, and 

 others; with the last joint produced into a needle-like 

 stabbing process in spiders). 



(6) Two rami developed (usually, but perhaps not always, 

 the equivalents of the endopodite and exopodite) supported 

 on the somewhat elongated corm (basal segment). This is 



