Embryo Project Encyclopedia Articles

For Thomas Hunt Morgan clarity was of utmost importance. He was therefore frustrated with the many disparate, disconnected terms that were used to refer to similar, if not the same, regenerative processes within organisms. When Morgan wrote Regeneration in 1901 there had been many different terms developed and adopted by various investigators to describe their observations. As a result there were many inconsistencies making it difficult to discuss results comparatively and also making it more challenging to generalize. Defining terms was a priority for Morgan. He appreciated the diversity of phenomena that had been studied and sought to develop language to facilitate further studies and interpretations.

Translational developmental biology is a growing approach to studying biological phenomena that explicitly aims to develop medical therapies. When discussing the generation of new therapies it is often argued that they will emerge as a "translation" from "fundamental biology." Although translational research is not a new term, "translational developmental biology" has been steadily gaining popularity as discoveries in cell and developmental biology, particularly those involving stem cells, provide a basis for regenerative medicine.

Dictyostelium discoideum is a cellular slime mold that serves as an important model organism in a variety of fields. Cellular slime molds have an unusual life cycle. They exist as separate amoebae, but after consuming all the bacteria in their area they proceed to stream together to form a multicellular organism. These features make it a valuable tool for studying developmental processes and also for investigating the evolution of multicellularity. Long thought to be a type of fungus, it has recently been shown that slime molds in fact bear no relation to fungi. Rather they form the monophyletic Mycetozoa, which consists of three distinct groups: plasmodial slime molds; cellular slime molds; and the Protostelia, all of which are structurally similar and consist of a fruiting body supported by a stalk. The cellular slime molds are characterized by a life cycle that includes periods of both multicellularity and unicellularity.

Throughout his long and fruitful career John Tyler Bonner has made great strides in understanding basic issues of embryology and developmental-evolutionary biology. Indeed, Bonner's work on morphogenesis highlighted synergies between development and evolution long before "evo-devo" became a part of the scientific lingua franca. Princeton University Press published his first book, Morphogenesis: An Essay on Development, in 1952. In his autobiography Lives of a Biologist, Bonner described his motivations for writing Morphogenesis as a book about developmental biology. He wanted to show how the methods of "old embryology" could be applied to all organisms.

Abraham Trembley's discovery of the remarkable regenerative capacity of the hydra caused many to question their beliefs about the generation of organisms. Born 3 September 1710 to a prominent Geneva family, Trembley studied at the Calvin Institute, now the University of Geneva, where he completed his thesis on calculus. He went on to become tutor for Count William Bentinck's two sons, and it was while teaching the boys natural history that Trembley came across a strange organism in a sample of pond water. This mysterious polyp, or hydra, had been previously described by Antoni van Leeuwenhoek, as well as an anonymous English gentleman in 1704, but Trembley was unaware of the polyp's identity and began a series of experiments to determine whether it was an animal or a plant. His investigations were also motivated by his observation that the number of arms on different polyps varied, an irregularity uncommon in animals. Yet Trembley felt that it was an animal.

Charles Manning Child designed an experimental test, the susceptibility assay, to measure the effects of different toxins on developmental processes. The susceptibility assay measured an organism s vulnerability to death when it was submerged in a noxious solution. The assay involved immersing an organism in a solution that contained a depressant or inhibitory substance, such as alcohol, and then measuring the responses of the organism. Child interpreted these measurements as revealing information about the relative levels of metabolic activity within the organism. Child predicted an organism's susceptibility to death should vary directly with its metabolic rate. An organism with a high metabolic rate would be expected to die more quickly in a noxious chemical solution than an organism with a lower metabolic rate: the higher the rate, the more quickly death should ensue. He also predicted young organisms should have higher metabolic rates than older organism, since children were known to metabolize drugs more quickly than adults.