Marvels of the Universe 883 
Zoéa turn into another creature known as Megalopa. 
But nobody took Slabber’s statement seriously 
until fifty-four years later, when Vaughan Thompson 
showed that Slabber was in the main correct, and 
that both Zoéa and Megalopa are stages in the 
evolution of the Crab. 
Even then, controversy raged warmly around 
the question whether this metamorphosis was 
general among the Crab kind, or restricted to a 
few special species. 
The fires of that controversy have died“out long 
since, and to-day we know that Crabs and Lobsters 
and their kind—with a few exceptions where the 
changes are undergone in the egg—pass through 
several larval stages of existence, corresponding to 
what were formerly known as distinct species under 
the names of Zoéa and Megalopa. The accom- 
panying illustration (page 882) will make this plain. 
It shows the successive stages in the infancy of the 
common Shore-crab. 
When one remembers that the eggs are about 
the size of a mustard-seed it will be realized 
that the larval Crabs on hatching are very 
minute and perfectly transparent—as, indeed, they 
remain until they develop true crab-shaped shells. 
In these earliest stages they are remarkable for 
having an enormous “ head,” and a long, thin tail. 
The “head” a little later produces a very long 
spine from its upper side. 
In the Megalopa stage there is a much 
nearer approach to normal crab-form, with large, 
stalked eyes, and nippers to the front pair of 
legs; but the long, slender ‘‘ tail” sticks out 
behind. 
All this time the larval Crab swims through the 
upper waters, where its transparency gives it a 
chance of escaping the numerous enemies that 
would feed upon it. When the last larval skin 
is thrown off, and an opaque “shell” takes its 
place, the miniature Crab sinks to the bottom 
and tucks its flattened tail tightly against the 
under-side of its body. As the Crab grows the 
shell becomes too small, and from time to time is 
thrown off, a new and at first soft shell having 
formed beneath the old one. Our illustration on 
this page shows the whole series of such shells 
that were thrown off successively by the same 
Shore-crab in its progress from infancy to adult 
life. 
TRANSFORMATIONS OF CRABS. 
The photograph represents fourteen empty shells, all 
cast off successively by the same individual Shore-crab to 
accommodate its increasing bulk. 
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