Every normal crustacean, on the other hand, has the abdominal region of the body covered by a thick chitinous shell. In the Hermits this is represented only by a thin and delicate membrane--of which the sorry figure the creature cuts when drawn from its foreign hiding-place is sufficient evidence. Any one who now examines further this half-naked and woe-begone object, will perceive also that the fourth and fifth pair of limbs are either so small and wasted as to be quite useless or altogether rudimentary; and, although certainly the additional development of the extremity of the tail into an organ for holding on to its extemporized retreat may be regarded as a slight compensation, it is clear from the whole structure of the animal that it has allowed itself to undergo severe Degeneration. In dealing with the Hermit-crab, in short, we are dealing with a case of physiological backsliding. That the creature has lost anything by this process from a practical point of view is not now argued. It might fairly be shown, as already indicated, that its freedom is impaired by its cumbrous exoskeleton, and that, in contrast with other crabs, who lead a free and roving life, its independence generally is greatly limited. But from the physiological standpoint, there is no question that the Hermit tribe have neither discharged their responsibilities to Nature nor to themselves. If the end of life is merely to escape death, and serve themselves, possibly they have done well; but if it is to attain an ever increasing perfection, then are they backsliders indeed. A zoologist's verdict would be that by this act they have forfeited to some extent their place in the animal scale. An animal is classed as a low or high according as it is adapted to less or more complex conditions of life. This is the true standpoint from which to judge all living organisms. Were perfection merely a matter of continual eating and drinking, the Amœba--the lowest known organism--might take rank with the highest, Man, for the one nourishes itself and saves its skin almost as completely as the other. But judged by the higher standard of Complexity, that is, by greater or lesser adaption to more or less complex conditions, the gulf between them is infinite.