Morphology. 63 
Birgus latro, which lives upon land and there feeds 
upon cocoa-nuts. The whole structure of this crab, it 
seems to me, unmistakeably resembles the structure _ 
of a hermit-crab (see drawings on the next page, 
Fig. 7). Yet this crab neither lives in the shell of | 
a mollusk, nor is the hinder part of its body in the soft 
and fleshy condition just described : on the contrary, it 
is covered with a hard integument like all the other 
parts of the animal. Consequently, I think we may infer 
that the ancestors of Birgas were hermit-crabs living 
in mollusk-shells; but that their descendants grad- 
ually relinquished this habit as they gradually became 
more and more terrestrial, while, concurrently with 
these changes in habit, the originally soft posterior 
parts acquired a hard protective covering to take the 
place of that which was formerly supplied by the 
mollusk-shell. So that, if so, we now have, within the 
limits of a single organism. evidence of a whole series 
of morphological changes in the past history of its 
species. First, there must have been the great change 
from an ordinary crab to a hermit-crab in all the 
respects previously pointed out. Next, there must 
have been the change back again from a hermit-crab 
to an ordinary crab, so far as living without the ne- 
cessity of a mollusk-shell is concerned. From an 
evolutionary point of view, therefore, we appear to have 
in the existing structure of Bzrgus a morphological 
record of all these changes, and one which gives us a 
reasonable explanation of why the animal presents the 
extraordinary appearance which it does. But, on the 
theory of special creation, it is inexplicable why this 
land-crab should have been formed on the pattern of 
a hermit-crab, when it never has need to enter the shell 
—~_)> 
