308 NATURAL HISTORY. 
shaped as to be fitted for digging as well as walking; 
and in others still they are armed with pincers, so as to 
be instruments of prehension as well as locomotion. In 
those Crustacea that swim, as Lobsters, Prawns, etc., 
the abdomen generally ends in a large fin-like expansion, 
which works up and down in swimming like the tail of 
the Whale. But in those which are to walk rather than 
swim, as the Crab, this part is small, and is bent up un- 
derneath. 
524. All Crustacea come from eggs. The eggs are 
commonly carried about adhering to the under part of the 
abdomen. This we often see in the Lobster. In a boil- 
ed Lobster they are red, and the mass is called the cor- 
al. More than twelve thousand eggs have been found 
attached to the abdomen of a single Lobster. 
525. There is not generally any true metamorphosis in 
this class. But in some, the animal, when first born, is 
entirely unlike the perfect animal. This is the case with 
the common Crab. In Fig. 240 you 
see a representation of the Crab when 
it first issues from the egg. The 
large figure is a magnified represent- 
ation, the natural size being given on 
the little scroll at the side of it. This 
is almost as unlike the mature Crab 
as the larva of the Musquito is unlike 
_ the Musquito itself (§ 502). 
526. In most of the Crustacea there 
is manifest the ring-like arrange- 
ment of segments which is so char- 
acteristic of the Articulata ($ 381). 
Fig. 240.—Fanly form of But in some it is so much modified 
Heer as not to be apparent without partic- 
ular observation. Thus,in the Crab, as we look on its 
broad carapace of shell, the ring-like arrangement seems 
to be entirely forsaken; but on examining closely, we 
find that this carapace is only an excessive enlargement 
