[17] OYSTER CULTURE. 769 
we will describe in the chapter in which we treat of the rearing of this 
mollusk. At other places they are taken from the sea and placed in 
salt marshes, since it has been noticed that a sojourn in water less salt 
than that of the sea improves their flavor. Finally, there are no places 
along our coast where this mollusk cannot be cultivated with advantage 
and profit, and our mauy railroad facilities will cause it to be still more 
widely known and esteemed throughout France. 
CRUSTACEANS. 
The important class of crustaceans constitutes one of the divisions of 
the sub-kingdom Articulata. The animals of this class are character- 
ized by a symmetrical body divided into a number of more or less similar 
segments, and provided with a nervous system, consisting of a row of 
ganglia, or small, nervous masses, connected by nerve cords and arranged 
in a longitudinal chain following the median line of the body, with a 
ganglion located in each segment. The appendages constitute a variable 
number of pairs, each pair being carried by a segment. Respiration is 
aquatic, or by means of gills; the skin is sometimes soft, and sometimes 
hard or coriaceous, forming an external skeleton moved by internal 
muscles. This last characteristic is peculiar to crustaceans, as is also 
the pyramid-like gills, furnished with hairs or little tufts, and placed 
on each side of the thorax at the base of the feet, or under the abdominal 
portion of the body. The segments of the body are generally twenty- 
one in number, but the first are nearly always united into a firm, inflexible 
portion, containing the head and thorax and named, accordingly, the 
cephalothorax. The remaining segments remain distinct and together 
form the abdominal portion of the animal. This division is very easily 
recognized in the crab and lobster, in which animals that portion which 
is popularly known as the tail represents the abdomen. The limbs of 
crustaceans number from five to seven pairs; those which are borne by 
the abdominal segment being generally only rudimentary and desig- 
nated false feet. These false feet subserve respiration, in some forms, 
and in others carry the eggs during incubation, as in the species to be 
mentioned farther on. The crustaceans are subdivided into several fami- 
lies, among which we shall call attention to those containing useful spe- 
cies, all of which belong to the same order, that of decapods (%<za, ten; 
mobs, feet). The name clearly indicates the distinctive character, that 
of having five pairs of feet. Of these five pairs, the anterior is often 
terminated, as in the cray-fish, crab, and lobster, by large and powerful 
pincers or claws, which are of use in prehension and in defense. A 
large abdomen, lengthened into a caudal appendage and terminating in 
a broad swimmeret, characterizes the macrurous decapods (2zpés, large; 
obpa, tail). When, on the contrary, it is short, flat, and recurved under 
the cephalothorax, it classes the animal among the brachyurous deca- 
pods (6pazis, short; va, tail), as the crab, &c. With these general de- 
finitions we can now pass to the consideration of those species which are 
S. Mis. 29-49 " 
