One of Thomas Hunt Morgan’s earliest experimental studies on regeneration was published in the Quarterly Journal of Microscopical Science in 1895. His research for this article, however, was focused not directly on the problem of regeneration in the living world but instead on the problem of metamerism in the earthworm, Allolobophora foetidus. The problem of metamerism, as Morgan understood it, was that certain organisms develop their body in units or segments (mers). Not every one of these segments of the body develops with the same structure and function. The fundamental question then is why, if development is a regular process, do the various segments of an animal body develop differently.
Earthworms have segments. Within earthworm segments the internal parts can vary from one segment to the next. Yet, there was one developmental process common across that variance. Morgan found through serial section experiments with earthworms, that the one common developmental process in animals was regeneration.
Morgan notes in this article that he began studying earthworms in the winter of 1887–8 and steadily developed that line of research over the years. When one of his students at Bryn Mawr College, Elizabeth Nichols, worked with him on this line of research, he began to more rigorously and systematically experiment. As the four plates included with this article demonstrate, his method was to think about all of the possible ways that he could systematically introduce abnormality through experiment. Then once he introduced abnormality, he patiently observed how a normal process of development, or organic generation, would respond to his introduced perturbations. Morgan’s method depended on the consideration of many alternative accounts of how variance within an organism might come about, given that the processes seemed to be regular and recurring across a variety of different animals.
Over his career, Morgan looked at regeneration in a variety of other organisms, including Oligochaete worms (Planaria maculata), Hydromedusa (Gonionemus vertens), Bipalium, Teleosts, Hermit-crabs, Tubularia, and many more. While Morgan is now known for having developed one of the most standardized and prolific laboratory critters for quantitative genetics—the fruit fly, Drosophila melanogaster—his early career shows anything but a devotion to any single experimental organism. Rather, his early career shows the development of a systematic way of doing experimental work and a curiosity about normal developmental processes (like regeneration) that trended across a variety of organisms.