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N« ZOOL. GAL.] NATURAL HISTORY. 
The Chilognatha , or lull 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 vege¬ 
tables, and some of the species emit a luminous secretion. 
The Chilopodes have a depressed membranaceous body, 
with a coriaceous 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 pal- 
piform appendages. They run very fast, living under 
stones, avoiding the light, and eating the remains of ani¬ 
mals. The larger species are dreaded in warm climates, 
and some are phosphorescent, as the genera Scutigera , 
Lithobius , and Scolopendra. 
The Crustacea, Cases 13 to 22, are the only Annu~ 
lose animals with jointed feet that respire by gills ; these 
gills are generally placed near the base of the legs, and 
are protected by the border of the thoracic shell, or 
carapace, but in a few they are external. They are the 
giants among the Annulosa, and all live in the water. 
Some few leave it for a short time in search of food, but 
they return to it to breed and respire. Many kinds are 
found in a fossil state. 
The more typical Crustacea have their eyes placed on 
a peduncle ( Podophthalma ) furnished with a facetted 
cornea, and the rings of the thorax are covered by a 
common shell. Among these, by far the greater number 
are called Decapodes, because they have five pairs of 
feet, with the gills at their base under the thorax, and 
five pairs of feet-like jaws. Their head is covered with 
the same hard common case as the thorax. 
The Crabs (Cases 3 to 19) differ from the Lobsters 
and Prawns in their caudal rings being less developed, 
and bent under the hinder part of the greatly expanded 
thorax. 
Amongst these short-tailed Crustacea are specimens of 
the Swimming Crabs, of the genera Portunus, Podopii - 
thalmus , &c. These animals have the posterior leg ter¬ 
minated by very flat joints, of an oval or orbicular form, 
and calculated to act as fins in swimming. The last pair 
