184 THE HISTORY OF CREATION, 
account of their delicate skill in weaving, the union of the 
joints of the trunk, or metamera, goes so far, that the trunk 
now consists of only two pieces, of a head-breast (cephalo- 
thorax) with jaws, feelers, and four pairs of legs, and of a 
hinder body without appendages, where the spinning warts _ 
are placed. In Mites (Acarida), which have probably arisen 
by degeneration (especially by parasitism) out of a lateral 
branch of Spinning Spiders, even these two trunk pieces 
have become united and now form an unsegmented mass. 
The class of Scolopendria, Myriapoda, or Centipedes, the 
smallest and poorest in forms of the four classes of 
Arthropoda, is characterized by a very elongated body, 
like that of a segmented Ringed worm, and often possesses 
more than a hundred pairs of legs. But these animals 
also originally developed out of a six-legged form of Trache- 
ata, as is distinctly proved by the individual development 
of the millipede in the egg. Their embryos have at first 
only three pairs of legs, like genuine insects, and only 
at a later period do the posterior pairs of legs bud, one by 
one, from the growing rings of the hinder body. Of the 
two orders of Centipedes (which in our country live under 
barks of trees, in moss, ete.) the round, double-footed ones 
(Diplopoda) probably did not develop until a later period 
out of the older flat, single-footed ones (Chilopoda), by 
successive pairs of rings of the body uniting together. 
Fossil remains of the Chilopoda are first met with in the 
Jura period. 
The third and last class of the Arthropoda breathing 
through trachee, is that of the Flies, or Insects, in the narrow 
sense of the word (Insecta, or Hexapoda), the largest of all 
