INSECTS AND THEIR NEAR RELATIVES . 
13 
Fig. 6 .—Lower side of 
cephalothorax of a 
spider: tnd, man¬ 
dible ; tttx, maxilla ; 
us ; /, lower 
sternum. 
dible: ; 
A palp* 
lip ; s y s 
appendages—two pairs of jaws, and four pairs of legs. The 
first pair of jaws are the mandibles (man'di-bles), the second, 
the maxillce (max-il'lse). 
The mandibles (Fig. 6, md) lie in front of and above the 
mouth, and consist each of two or three segments. The\ 
serve for seizing prey, and often also for 
killing it. In many books they are termed 
the chelicerce (che-lic'e-rae). 
The maxillce (Fig. 6, nix') lie just behind 
the mandibles, one on each side of the 
mouth. Each maxilla bears a large feeler 
or palpus (Fig. 6,/). These palpi vary 
greatly in form; frequently they resemble 
legs; hence many Arachnida appear to 
have five pairs of legs. The palpi are often 
so largely developed that each maxilla ap¬ 
pears to be merely the first segment of its 
leg-like palpus. These appendages are often 
called the pedipalpi (ped-i-pal'pi). But as the 
name Pedipalpi is applied to one of the or¬ 
ders of the Arachnida, we will call these ap¬ 
pendages the palpi. 
The legs of Arachnida consist typically of 
seven parts (Fig. 7), which are named, begin¬ 
ning with the one next to the body, as fol¬ 
lows : r, coxa (cox'a); 2, trochanter (tro-chan'- 
ter); 3, femur (fe'mur); 4, patella (pa-tel'la); 
5, tibia (tib'i-a) ; 6, metatarsus (met-a-tar'sus); 
and 7, tarsus (tar'sus). The tarsus may be composed of 
several segments, and is usually furnished with claws. 
Two forms of breathing organs are found in this class : 
one, tracheae, resembling the tracheae of insects, described 
in the chapter on the anatomy of insects ; and the other, 
tracheal lungs or lung sacs, which consist of many leaf-like 
plates enclosed in a sac. Both forms open by paired spira¬ 
cles, which are usually situated on the lower side of some of 
the abdominal segments. 
