XX INTRODUCTION. 
furnished with antennae, eyes, and mouth ; and their bodies are 
covered with a crust or shell, divided into segments by trans- 
verse incisions, the segments being united by a strong mem- 
brane. The crust turns red by boiling, whatever colour it 
may have borne while the animals were in a living state. 
Once a year these animals moult, throwing off their old crust 
or shell, and forming a new one, the animal remaining in a 
naked, and greatly weakened state, during the intermediate 
time. The Crustacea swim with great ease, but on land their 
motions are generally cramped and awkward ; and they are 
confined to crawling, or leaping by means of the tail. "When 
a limb is injured they possess the extraordinary power of 
throwing it off, and forming a new one. Another singular 
property which they possess is that of emitting light. It is 
well known that the shell of a lobster, or crab, when begin- 
ning to decay, emits light ; and there is a smaller kind of 
crab, called cancerfulgens, which produces a luminous effect 
when alive. The Crustacea lay eggs, and the young of some 
of the species undergo a transformation before they attain 
their full size. The Crustacea were divided into two sec- 
tions and seven orders by Cuvier, which are as follows : 
SECTION I. Malacostraca. 
Shell solid, legs ten or fourteen, foot-jaws six or ten, mandibles 
two, maxillae four ; mouth with a labrum. 
Sub-section 1. Podophthalma, eyes on foot-stalks. 
ORDER 1. Decapoda, legs ten. 
Sub-order 1. Brachyura, the crabs. 
Sub-order 2. Macroura, the lobsters. 
ORDER 2. Stomapoda, legs more than ten. 
Sub-section 2. Edriophthalma, eyes not on foot-stalks. 
ORDER 3. Amphipoda, body compressed; mandibles palpigerous. 
ORDER 4. Lamodipoda, abdomen rudimental, with only the rudi- 
ments of one or two pairs of appendages. 
ORDER 5. Isopoda, body depressed; abdominal appendages flat; 
mandibles not palpigerous. 
SECTION II. Entomostraca. 
Shell not solid ; legs variable in number ; mouth variable. 
ORDER 6. Branchiopoda. Integuments horny, branchiae feathery, 
forming part of the feet. 
ORDER 7. Pcecilopoda, mouth suctorial. 
Sub-order 1. Xiphosura, or king-crabs. 
Sub-order 2. Siphonostoma, or fish parasites. 
Lamarck divides the Crustacea, into only the two following orders, 
viz. 
1 The Homobranchia, which have the body covered with an entire 
