LOBSTERS, CRABS, SHRIMPS, ETC.; 
CRUSTACEA. 
A VETO now completed our brief survey of the insects, we proceed to the Crus- 
tacea, a very large class, in which are included the lobsters, crabs, shrimps, 
water-fleas, and a host of other familiar beings. Even the Cirrhipeds, popularly 
known under the name of Barnacles, are members of this large class, and a number 
of curious animals, which have until lately been classed with the spiders, are now 
ascertained to belong to the Crustacea. 
These beings can be easily separated from the insects on account of their 
general structure, the head and throat being fused into one mass, called technically the 
cephalo-thorax ; the number of limbs exceeding the six legs of the insects ; and the mode of 
breathing, which ris by gills, and not by air-tubes. As a necessary consequence of the last- 
mentioned structure, the Crustaceans possess no spiracles, such as are found in all the stages 
of insect life, from the larva to the imago. They undergo a well-marked metamorphosis, and 
in those creatures whose development is best known, the change of shape is so entire as to 
have led the earlier zoologists to consider the undeveloped Crustacea as separate species. They 
may be also distinguished from the spiders by the presence of a series of feet, or rather of 
locomotive organs arranged under the abdomen, as well as by the metamorphosis of their 
earlier stages, a phenomenon which is not known to take place among the spiders. 
The name of Crustacea is sufficiently appropriate, and is given to these creatures on 
account of the hard shelly crust with which their bodies and limbs are covered, a covering 
which, in some cases, is of such flinty hardness as to be used for the purpose of sharpening 
knives, and in others, attains a glossy polish which reminds the observer of glazed porcelain. 
As our space is rapidly diminishing, we must proceed at once to the different families and 
genera, simply noting the more important characteristics as we proceed through the class. 
TEN-LEGGED CRUSTACEANS; DECAPODA. 
The first section of these creatures are called the Podoptlialmata, or Stalk-eyed Crus- 
taceans, because their eyes are set upon footstalks. The first order is that of the Ten-legged 
Crustaceans, so called on account of the five pairs of legs that are set in each side. These 
are exclusive of the complicated apparatus of the mouth, and the jaw-feet which guard its 
entrance. The Crabs are placed first in the list of Crustaceans, and are technically called 
Brachyura, or Short-tailed Crustaceans, because their tails are of comparatively small size, and 
are tucked under the large shielded body. In the preliminary stages, however, the Crabs have 
tails as proportionately long as those of a lobster or a cray fish. 
