And this combined testimony of a number of organs in the same organism is what the theory of descent would lead us to expect, while the rival theory of design can offer no explanation of the fact, that when one organ shows a conspicuous departure from the supposed ideal type, some of the other organs in the same organism should tend to keep it company by doing likewise. [4] It is, however, probable that all species of the genus retained a tiny rudiment of wings in greatly dwindled scapulo-coracoid bones. And Mr. H. O. Forbes has detected, in a recently exhumed specimen of the latter, an indication of the glenoid cavity, for the articulation of an extremely aborted humerus. (See _Nature_, Jan. 14th, 1892.) [Illustration: FIG. 6.--Skeleton of _Dinornis gravis_, 1/16 nat. size. Drawn from nature (_Brit. Mus._). As separate cuts on a larger scale are shown, 1st, the sternum, as this appears in mounted skeletons, and, 2nd, the same in profile, with its (hypothetical) scapulo-coracoid attached.] As an illustration both of this and of other points which have been mentioned, I may draw attention to what seems to me a particularly suggestive case. So-called soldier-or hermit-crabs, are crabs which have adopted the habit of appropriating the empty shells of mollusks. In association with this peculiar habit, the structure of these animals differs very greatly from that of all other crabs. In particular, the hinder part of the body, which occupies the mollusk-shell, and which therefore has ceased to require any hard covering of its own, has been suffered to lose its calcareous integument, and presents a soft fleshy character, quite unlike that of the more exposed parts of the animal. Moreover, this soft fleshy part of the creature is specially adapted to the particular requirements of the creature by having its lateral appendages--i. e. appendages which in other crustacea perform the function of legs--modified so as to act as claspers to the inside of the mollusk-shell; while the tail-end of the part in question is twisted into the form of a spiral, which fits into the spiral of the mollusk-shell. Now, in Keeling Island there is a large kind of crab called _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 _Birgus_ were hermit-crabs living in mollusk-shells; but that their descendants gradually relinquished this habit as they gradually became more and more terrestrial, while, concurrently with these changes in habit, the originally soft posterior