CirutiPEDiA. CRUSTACEA. UEPAuiuAi. 
293 
Etituting the tail. The tlioracic legs are six pairs in 
numhe7-, in the female all terminated b}'- a double claw, 
serving both as organs of motion, prehension, and mas- 
tication. The abdominal legs are also six pairs, folia- 
ceous in structure, and serving the purpose of swim - 
ming and respiration. The nervous system consists 
of a principal medullary mass, which surrounds the 
oesophagus like a ring, giving otf nerves to the parts 
belonging to the head and thorax ; and a large cord 
which extends from this downwards along the median 
line of the abdomen, sending off nerves to the abdominal 
regions and the tail. 
Limulus, King-crab. — This is the 
only genus belonging to the Xiphosura, 
and the species are not numerous. Some, 
however, are of laige size, occasionally 
attaining the length of two feet. They 
are all marine, inhabiting the seas of 
India, China, Japan, and the coasts of 
North America. Thej’ seem to prefer 
living on sandy shores ; and in order to 
avoid the great heat of the sun, which 
proves fatal to them, they bury them- 
selves in the mud. The young undergo 
considerable changes in their progress 
to maturit}'; for at first they have no 
tail, their abdominal buckler is rounded posteriorly, 
and the sixth pair of abdominal legs are undeveloped. 
The male is distinguished from the female by the 
first and second pairs of thoracic feet being swollen, 
and moreover destitute of the didactyle claw. The 
long tail of one of the species from the Moluccas is 
used by the natives as a point for their arrows, and the 
wounds caused by them are said to be dangerous. In 
America, where they are common, the large shehs are 
used by the inhabitants to lade water with, and the 
animals themselves are used to fatten pigs. In China 
the eggs are used as food by the natives, and in Japan 
a species is figured in their primitive zodiac as the 
Fig. 199. 
Limnliis moluccanus 
representative of the constellation Cancer. The species 
here represented (fig. 199 ) is Limulus moluccanus. 
Class — CIRRIPEDIA (Barnacles, or Sea-acorns). 
The Cirripeds are now universally admitted to be 
Crustaceans, though till lately they used to be classed 
with the Mollusca, on account of their shells. 
They are articulated animals, contained within a 
hard covering composed of several pieces, and consist- 
ing of laminae of calcified chitine. The body of the 
animal is inclosed in a sac lined with a most delicate 
membrane of chitine, which in one group is prolonged 
into a peduncle and contains the ova. It is distinctly 
articulated, and is placed with the back downwards. 
The part which is called the abdomen has two rows of 
fleshy lobes, each furnished with long horny appendages, 
provided with many-jointed curled hairs or cirrhi to 
the number of twelve pairs, which are constantly being 
protruded and withdrawn again through an aperture in 
the shell. Thej' are the feet of the animal transformed 
into these organs, and by means of them a current is 
produced in the water, which attracts to the mouth the 
objects which serve as food,. The Cirripeds have man- 
dibles and jaws very similar to other Crustacea, and 
recent observations prove them to be possessed of eyes. 
Their nervous system is ganglionic; they have a double 
circulation of blood; and they respire by means of 
branchiae or gills, the form of which varies. The greater 
part of them are hermaphrodite. Like the majority of 
the Entomostruca, to which they are closely allied, the 
young undergo gieat changes in their progress to 
maturity. When first hatched from the egg they are 
exceedingly small ; but when they have increased in 
size, they resemble the larvae of the Cyclops. They 
float freely in the sea, swimming rapidly with their 
back downwards. They soon become invested with a 
coriaceous shell, and they now begin to look out for a 
fit place to which they may attach themselves. Hav- 
ing found this, they adhere to it by the part of the body 
near the head, and in a few da 3 's afterwards they throw 
off their external covering. The shelly valves then 
form, consisting at first exclusively of chitine ; the 
antennae disappear, being cemented to the surface of 
attachment ; the eyes remain, but in a more or less 
rudimentary form ; three more pairs of legs are developed, 
and then the animal assumes its perfect state. During 
this time the Cirriped, like the other Crustacea, espe- 
cially the Entomostraca, throws off its covering or 
moults at frequent intervals, and is very rapid in its 
growth. 
The greater part of the Cirripeclia are arranged in 
two large families — the Pedunculated Cirripeds, or 
Lepadid.® ; and the Sessile Cirripeds, or Balanida:. 
I. LEPADIDH5 {Pedunculated Cirripeds, oi 
Barnacles). 
The LepadidcB are characterized by having a length- 
ened peduncle, which is coriaceous, hollow, flexible, 
and provided with muscles, by means of which they 
attach themselves to submarine bodies. The species 
are tolerably numerous, and are found extending over 
