152 
NATURAL HISTORY. 
[n. ZOOL. GAL. 
of the upper wing is like parchment or leather, and the other half mem¬ 
branaceous, like the lower pair, are in the 11th Case, as the Shield-bugs, 
Fire-flies ( Fulgora ), &c. 
The Apterous, or Wingless Insects, generally have four or five 
pairs of legs, and sometimes many more. They are always destitute of 
wings; and the chief alteration that takes place in their approach to¬ 
wards maturity, is, that they gain additional legs; this change sometimes 
takes place at a very early age, which has caused some naturalists to be¬ 
lieve that they do not undergo any metamorphosis. 
The Arachnida ( Cases 11 and 12) differ from the true insects in the 
head and thorax being united into a single mass, as well as in having 
more numerous legs and no wings. Some have pulmonary sacs, which 
fulfil the functions of lungs, with a heart, veins, and very distinct vessels : 
these have six or eight simple eyes, and from the manner in which they 
respire, are called Pulmonarice, as the various kinds of true Spiders. 
By the side of the kind of Spider that forms it, is placed the tubular 
case of one of the earth spiders, which forms a door to its tube that falls 
down to close the cavity when the animal is within. The other Arach¬ 
nida respire by tracheae, or air tubes, which traverse their body, as is 
the case with insects in general. The organs of circulation are wanting 
or very incomplete. They have two, or at most but four, simple eyes, 
and have been called Trachearice . Among these are the Tarantula , 
Scorpions, &c. 
The Myriapodes, or Centipedes, are so called on account of the 
number of their legs. They have generally twenty-four or more, ar¬ 
ranged along the entire length of the body, on a series of rings, each 
bearing one or two pairs. The first, and in several even the second 
pair of legs seem to form a part of the mouth. 
These animals bear some resemblance to little snakes and Nereides, 
from their feet being so closely applied to each other through the whole 
extent of the body. The number of the rings and the feet increases 
with age, a character which distinguishes them from the true Insects, 
which always have the same number of rings from their being first 
hatched to their adult state; all the true legs, which are furnished with 
hooks, are developed at. once, either when they are hatched or when 
they pass into the Pupa state, while the Myriapodes , when they leave 
the egg, are destitute of these organs. The Myriapodes live and in¬ 
crease in size longer than most other terrestrial Annulosa, for according 
to Savi, they require two years before the reproductive organs are de¬ 
veloped. They are divided into two orders, which have very distinct 
external characters. 
The Chilognatha, or Iuli of Linnaeus, have a cylindrical crustaceous 
body with clavate tentacles, formed of seven joints, and two thick jaws 
without palpi, as the genera Glomeris, lulus , and Polydesmus. They 
are slow-gliding animals, and roll themselves up spirally, or into a ball. 
They feed on dead and decomposed animals and vegetables, and some of 
the species emit a luminous secretion. 
The Chilopedes have a depressed membranaceous body, with a co¬ 
riaceous plate on the back of each ring, the last bearing a pair of long 
tail-like legs. Their antennae are slender, tapering at the tip. Their 
jaws bear little palpiform appendages. They run very fast, living under 
stones, avoiding the light, and eating the remains of animals. The 
