294 THE AMERICAN NATURALIST. (Vor. XXXIX. 
anterior side eyes, etc. Sometimes the most posterior eyes are 
called the dorsal eyes. An eye-row is either straight or curved. 
When the S. E. of a row are farther back than the M. E. of 
that row, the row is said to be recurved ; when the S. E. are 
more forward, the row is procurved. Dark-colored eyes are con- 
sidered to be diurnal in function, and pale eyes nocturnal. 
Many spiders have both kinds and the difference in appearance 
of the two is often very striking. 
The arrangement of the eyes 
is of the greatest importance 
in systematic araneology. The 
space between theanterior eye- 
row and the front or clypeal 
margin of the cephalothorax is 
called the clypeus, or fillet. 
Attached just below the clypeal 
margin are the mandibles, jaws, 
falces, or chelicerze, as they are 
variously termed. Each is of 
two parts: the basal joint, or 
larger part, and the fang, or api- 
cal part. The fang fits down 
into a groove of the basal joint, 
which is often margined with a 
few small teeth. The poison 
s glands open near the tip of the 
ro. ENS fang 4, mandible; c, maxilla; fang. The mandibles are usually 
et od vertical, sometimes uplifted, or 
tralis; x, spinnerets; s, coxa; 4, femur; v, pa- porrect. | Sometimes they are 
uds divergent, and in some cases the 
basal part is swollen above in 
front, and the mandible is then said to be geniculate. At the 
outer base of each basal joint there is, in some families, a small 
area separated from the rest of the surface; this is styled the 
boss, or lateral condyle. 
The mouth-parts seen from below are a median piece, the lip 
or labium, and a piece on each side, the maxille, or endites. 
In some cases the maxillae show an oblique furrow or impres- 

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