CRABS, LOBSTERS, SHRIMPS, WOOD-LICE, BARNACLES 273 
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They are nearly all aquatic animals, by far 
the larger portion being marine, and they 
breathe with gills. They are provided with | 
a hard calcareous or horny covering. The 
head is not separated from the trunk, as in 
insects; and they are provided with a num- 
ber of jointed organs, usually classified as 
three pairs of jaws, three pairs of foot-jaws, 
and five pairs of legs in the more typical | 
families; but in the smaller and more aber- 
rant species the number is more variable. 
In their early stages they frequently pass 
through very extraordinary changes of form, 
but after assuming their adult shape they 
grow by casting their shells at intervals. 
We will now notice a few typical | 
examples of the different groups of these 
creatures. 
The BRINE-SHRIMP is a little reddish 
creature about half an inch long, which 
prefers the concentrated solution of brine-pits to sea-water. It has eleven pairs of legs, and, 
notwithstanding its name, the front portion of its body is considerably broader and flatter in 
proportion than that of a real shrimp, the other half consisting of a jointed tail. 
BARNACLES were formerly considered to be shell-fish, but are now usually classed with the 
crabs and lobsters, because, when they are young, they appear as freely swimming creatures, 
with one eye, two antennz, and six pairs of jointed limbs. When they grow larger, they fix 
themselves to a rock or some other object by the head, and develop a shell, usually composed 
of several pieces. The commonest is the ACORN-BARNACLE, the white shell of which, measur- 
ing rather less than an inch across, swarms on rocks at the seaside. It is shaped like a limpet, 
but open at the top. The GOOSE-BARNACLES hang down by a stalk, and their jointed sheils 
more resemble those of a mussel than that of a limpet, though they are composed of several 
pieces. Various species similar to both those mentioned are found on piers, rocks, the bottoms 
of ships, and even sometimes on the skin of whales. 
In dark cellars in the country, under loose bark, or under pieces of wood which have been 
left in the fields, we often see creeping about brown creatures 
| about half an inch long, with jointed bodies and antennz, and 
| short jointed legs. They are called WoOoD-LICE, and several 
| species roll themselves up into a ball when alarmed. These 
| creatures feed chiefly on decaying vegetable substances; and 
| there is a larger marine species much like them, which is common 
in holes and crannies in the rocks on the seashore. 
There are other curious creatures, called WHALE-LICE and 
FISH-LICE, which are parasitic in their habits. Some of these 
look like spiders, and one or two have enormously long legs; 
but others are of strange and almost indescribable forms, and 
sometimes without legs at all. One species, found on the sprat, 
has two long appendages at the end of its body not unlike a 
pair of compasses. 
Photo by W. P. Dando, F.Z.5.] [Regent's Park 
ACORN-BARNACLE 
The general appearance is so different from the Stalked Barnacle that it 
is difficult to believe the two belong to the same group 
mary a ae sf 
PRE TE na Fei SHRIMPS and PRAWNS are red when cooked, but when alive 
egent f ar. . . . 
WOOD_LOUSE are very pretty semi-transparent objects, which may be seen 
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Ae remabieef a meron RNIN about through the glass of aquariums placed against 
marine group the wall. Prawns are larger than shrimps, and have a strong 
