243 
OHAP, 2th 
CRUSTACEA. 
CRABS—LOBSTERS. 
How are they distinguished from the Insects ?— Barnacles and Acorn-shells.— 
Siphonostomata.—Entomostraca.—King-Crab.—Edriophthalmia.—Sandhoppers. 
—Thoracostraca.—Compound Eye of the higher Crustaceans. — Respiratory 
Apparatus of the Decapods.—Digestive Organs.—Chele or Pincers.—Distribu- 
tion of Crabs.—Land Crabs.—The Calling Crab.—Modifications of the Legs in 
different species.—The Pinna and Pinnotheres.—Hermit Crabs.—The Lobster. 
—The Cocoa-nut Crab.—The Shrimp.—Moulting Process.—Metamorphoses of 
Crabs.—Victims and Enemies of the Crustaceans—Their Fecundity.—Matine 
Spiders and Insects. 
Tue Crustaceans were included by Linnzus among his insects, 
but their internal structure presents such numerous and im- 
portant differences that modern naturalists have raised them to 
the dignity of a separate class. They have indeed, in common 
with the insects, an articulated body, generally cased with hard 
materials; they are like them provided with jointed legs, with 
antenne or feelers, and their organs of mastication are similarly 
formed; but insects breathe atmospheric air through lateral 
pores or trachee, while the crustaceans, being either aquatic 
animals or constantly frequenting very damp places, have a 
branchial or a tegumentary respiration. The perfect insect 
undergoes no further change; the crustacean, on the contrary, 
increases in size with every successive year. The higher crus- 
tacean possesses a heart, which propels the blood, after it has 
been aérated in the gills, to every part of the body ; in the insect 
the circulation of the blood is by no means so highly organised. 
On the other hand many of the insects are far superior in point 
of intelligence to even the best endowed crustaceans, for here 
we find no parental care, no mutual affection, no joint labours 
for the welfare of a large community, no traces of an amiable 
