L.kmodipods. CRUSTACEA. Isorous. 289 
They are found in great numbers under stones, or 
under the decaying sea-weeds thrown up on the beach 
by the tide, and when dis- 
turbed leap with great 
agility. At times they occur 
in such countless swarms 
as to give the appearance of 
at tbe extremities of six pairs of members attached to 
the abdominal segments, and called false feet. The 
number of true feet are seven pairs, which are almost 
always terminated by a somewhat sharp and often 
more or less prehensile claw. The females carry their 
eggs under the thorax, in a pouch attached to the base 
of the feet. They are retained there till the young 
^ W a thick mist at the water’s 
are hatched, and the mother then opens the pouch 
^ ' ^ as they bound into the 
and allows them to make their escape. This order 
air to a considerable height. 
contains many species, which are distributed over a 
1 1 The species we give as a 
wide range. They may be divided into three large 
Common sandhopper, representative of the genus 
groups: — 
and of the order, is the 
The first group are termed the Walking Isopods. 
Talitrua locuata or saltator. — See fig. 187. 
They have their feet fitted chiefly for walking, and 
not adapted for swimming. Representatives of this 
group are the Sea Centipedes {Idotea) ; the Screws, 
Order II. — THE LHUMODIPODS {Laemodipoda), 
as they are generally called (Asellus), the various 
species of which live in fresh water; and the Wood 
lice (Oniscus) which are formed exclusively for living 
In this order the branchiae or gills are vesicular, as 
on dry land. 
in the Amphipods, but are only attached to the second 
The Limnori^ belong also to this group. There 
and third, more rarely the first, thoracic rings. The 
is only one species (^Limnoria terebrans — see fig. 189), 
segments of the thorax are six in number, and the feet 
but it is well known for its destructive habit of 
vary from five to seven pairs. The first is attached to 
the head, and, as well as the second pair, are ter- 
Fig. 189. Fig. 190. 
minated by prehensile claws, while the others are 
provided with a hook, flexible and more or less pre- 
hensile. The abdomen is reduced to such a rudi- 
mentary state that it is scarcely visible, being little else 
than a tubercle. The females carry their ova as the 
Amphipods do. The species belonging to this order 
are few in number, and none of them are large. 
Some of them have the body cylindrical in shape, the 
legs long and very slender, and they live free and un- 
attached, as the Skeleton Shrimps {Caprella), which are 
found amongst marine plants, creeping along in the 
same way as the “looping caterpillars,” often bending 
Boring Limnoria (Limnoria Sea Pill-ball (Spliaaroma 
terebrans). serratum). 
themselves back with great rapidity, and applying their 
boring into submersed timber. It is very small, sel- 
antennae to various parts of their body, while in swim- 
dom exceeding two-tenths of an inch in length ; but 
miug they bend the two ends of the body downwards. 
it is gregarious, and very abundant in some situations. 
Others have the body 
It is marine, and is generally found living in holes in 
Fig. isa. much developed, fiat. 
wood, which it forms for itself. The ravages this little 
and broad, the feet 
creature commits in the timber forming piers, dock- 
thick and hooked at 
gates, &c., are very great. It was first particularly 
JlJj ^ their extremity, and 
noticed by the late Mr. Stephenson, the eminent 
they live parasitical 
engineer, while engaged in the erection of the Bell 
upon other animals. 
Rock Lighthouse. Since then it has been observed 
Such are the Whale- 
in several other parts of our coasts, and has been the 
lice (^Cyamus), which 
cause of most serious injury to piles of wood support- 
Caprelia linearis — Male and Female. ^1'6 g6nerally found 
ing various useful erections on the shores of the sea. 
attached to the bodies 
The galleries which it forms in the wood are tortuous. 
of whales, and are occasionally seen in such numbers 
and run in all directions, though generally the animal 
upon them, that the individuals so infested are recog- 
bores upwards at an angle of about 45°. By being 
nized at a considerable distance by the white colour 
thus bored throughout its substance, the wood becomes 
thus imparted to them by the parasites. 
so disintegrated that the sea washes away its surface, 
As an illustration of this order we subjoin a figure of 
layer after layer, and the whole piece of timber is soon 
Cuprdla linearis, the Skeleton Screw. — See fig. 188. 
destroyed. 
The second group are termed the Swimming Iso- 
Order III.— THE ISOPODS (Isopoda). 
pods. The species belonging to it have their feet more 
or less adapted for swimming, and the last segment of 
the abdomen forms with the horizontal plates with 
The Isopods have their branchiae or gills in the form 
which the sixth pair of false feet are terminated a large 
of large, oval, more or less membranous plates, placed 
caudal fin. 
1 
VoL. II. 93 
