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“ TERRA NOVA ” EXPEDITION. 
to that of the Dromiacea and Dorippidae of carrying their shelter with them by 
means of the hinder lews, and on the other to that of the free-wandering crabs. But 
none of these organisms lives in a habitat locally removed from that of other Reptantia. 
Crabs and lobsters, Porcellanopogurus and ordinary hermit-crabs may be taken in the 
same locality. It is with their habits rather than with their habitats that their 
structure is correlated. Nor is it possible, in view of the fact that they possess free 
larvae, and those of the same type, and therefore persistent from their common 
ancestor, to construct any hypothesis which shall account for their unlikeness by 
supposing that at some former time they were isolated in unlike conditions of life. 
They owe their differences to themselves alone. 
There are few better instances than those afforded by carcinization of the fact that, 
the organism is, after all, the dominant factor in evolution. What is bred in the bone 
will come out in the flesh, and Nature is no more able than Man to make silk purses 
out of sows’ ears. 
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