CHAPTER VI. 
Jointed Animals,— continued . 
Centipedes, Millipedes, Scorpions, and Spiders, —Classes 
Chilopoda, Diplopoda, Arachnida, etc. 
Characters of According to modern views, centipedes are regarded as near allies 
Centipedes. 0 f insects, the chief differences between the two groups being that 
whereas in the latter there are only three pairs of jaws attached to the lower 
surface of the head, in the former four pairs of appendages are modified to act 
as masticating organs. Moreover, the body of an insect is sharply divided 
into an anterior portion, or thorax, bearing three pairs of walking legs, and a 
posterior half, or abdomen, which in the adult at least is not provided with 
locomotor limbs, but the body of a centipede is composed of a large and varying 
number of segments, substantially alike in structure, and each bearing a single 
pair of legs. The number of segments varies from fifteen to considerably over 
one hundred, yet no matter how many pairs of legs there may be—whether it be 
fifteen or one hundred and twenty-one—their number is invariably odd. 
The head bears a pair of elongate antennae in front, and often eyes arranged 
in two clusters at the sides. On its lower surface may be seen the four pairs 
of jaws. The first pair, or mandibles, are two-jointed and have a biting edge; 
the second pair, or maxillae, are soft, leaf-like, and united together in the middle 
line, each consisting of an outer jointed and an inner unjointed branch. The third 
pair, known as the first maxillipedes, are composed of four or five segments, and 
much resemble one of the walking limbs, being tipped with a claw. The fourth 
pair, or second maxillipedes, are large, powerful, and project forwards below the 
rest, so as more or less to conceal them from view. Their basal segments are 
usually fused to form a massive coxal plate, while the rest of the jaw consists of 
four segments, the terminal one being a long fang with a minute aperture at the 
tip, through which exudes poison secreted by a gland lodged inside the appendage. 
These two pairs of maxillipedes do not strictly belong to the head, since the dorsal 
elements of the segments that bear them are either distinct, or are united with 
the tergal plate of the following segment to constitute a. massive basilar plate. 
The rest of the body is composed of a varying number of segments, each 
consisting externally of a dorsal plate or tergum, and a ventral plate or sternum, 
connected laterally by a softer pleural membrane, to which the legs are articulated. 
These latter are usually short, composed of six or seven segments, and each is tipped 
with a single claw, and often furnished in addition with spines. The last pair are 
generally longer and stronger than the rest, and sometimes considerably modified 
