NATURAL HISTORY. 
79 
ROOM IV.] 
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 increase in size longer than most other terrestrial 
Annulosa, for according to Savi, they require two years 
before the reproductive organs are developed. They are 
divided into two orders, which have very distinct external 
characters. 
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 jaw T s. Their head is covered with 
the same hard common case as the thorax. 
