One reason which makes a zoologist certain that the Sacculina is a degenerate type is, that in almost all other instances of animals which begin life in the Nauplius-form--and there are several--the Nauplius develops through higher and higher stages, and arrives finally at the high perfection displayed by the shrimp, lobster, crab, and other crustaceans. But instead of rising to its opportunities, the sacculine Nauplius having reached a certain point turned back. It shrunk from the struggle for life, and beginning probably by seeking shelter from its host went on to demand its food; and so falling from bad to worse, became in time an entire dependant. In the eyes of Nature this was a twofold crime. It was first a disregard of evolution, and second, which is practically the same thing, an evasion of the great law of work. And the revenge of Nature was therefore necessary. It could not help punishing the Sacculina for violated law, and the punishment, according to the strange and noteworthy way in which Nature usually punishes, was meted but by natural processes, carried on within its own organization. Its punishment was simply that it was a Sacculina--that it was a Sacculina when it might have been a Crustacean. Instead of being a free and independent organism high in structure, original in action, vital with energy, it deteriorated into a torpid and all but amorphous sac confined to perpetual imprisonment and doomed to a living death. "Any new set of conditions," says Ray Lankester, "occurring to an animal which render its food and safety very easily attained, seem to lead as a rule to degeneration; just as an active healthy man sometimes degenerates when he becomes suddenly possessed of a fortune; or as Rome degenerated when possessed of the riches of the ancient world. The habit of parasitism clearly acts upon animal organization in this way. Let the parasitic life once be secured, and away go legs, jaws, eyes, and ears; the active, highly-gifted crab, insect or annelid may become a mere sac, absorbing nourishment and laying eggs."[95] There could be no more impressive illustration than this of what with entire appropriateness one might call "the physiology of backsliding." We fail to appreciate the meaning of spiritual degeneration or detect the terrible nature of the consequences only because they evade the eye of sense. But could we investigate the spirit as a living organism, or study the soul of the backslider on principles of comparative anatomy, we should have a revelation of the organic effects of sin, even of the mere sin of carelessness as to growth and work, which must revolutionize our ideas of practical religion. There is no room for the doubt even that what goes on in the body does not with equal certainty take place in the spirit under the corresponding conditions.