These stimulating researches into the sources of crime led to a controversy which reached its height two decades ere the treatise of Morel. To this controversy three suggestive works owed their origin: a psychological treatise by Dr. Lauvergne[14] on felons, a romance with a purpose by Eugène Sue,[15] and a suggestively practical brochure by a rather corrupt police official, Vidocq.[16] Seemingly conflicting as were these productions, all strikingly illustrated the influence of heredity and environment in the production of defectives. To these productions were soon added those of Moreau (de Tours),[17] Attemyer, Eliza Farnham,[18] the American Sampson,[19] Dally, Lélut, Camper, and the older Voisin. Morel[20] laid the foundation of what is widely known as the Lombroso School by a brochure wherein he proposed to entitle morbid anthropology, "that part of the science of man the aim of which is to study phenomena due to morbid influences and to malign heredity." To the factor of atavism, inconsistently ignored by Morel, the early embryologic studies of Von Baer and the biologic studies resultant on the transmutation of species lent special emphasis. Three possibilities of life await, as Wilson[21] remarks, each living being: either it remains primitive and unchanged, or it progresses toward a higher type, or it backslides and retrogresses. The factors underlying the stable state force the animal to remain as it is; those underlying the progressive tendency make it more elaborate, while the factors of degeneration, on the other hand, tend to simplify its structure. It requires no special thought to perceive that progress is a great fact of nature. The development of every animal and plant shows the possibilities of nature in this direction. But the bearings of physiological backsliding are not so clearly seen. That certain animals degenerate or retrogress in their development is susceptible of ready and familiar illustration. No better illustration is needed than is derived from the domain of parasitic existence. When an animal or plant attaches itself partly or wholly to another living being, and becomes more or less dependent upon the latter for support and nourishment, it exhibits, as a rule, retrogression and degeneration. The parasitic "guest" dependent on its "host" for lodging alone, or it may be for both board and lodging, is in a fair way to become degraded in structure, and, as a rule, exhibits marked degradation where the association has persisted sufficiently long. Parasitism and servile dependence act very much in structural lower life as analogous instances of mental dependence on others act on man.