This proposal seeks to explain movements of the body of the leech, Hirudo medicinalis, in terms of the forces generated by its muscles and by the arrangement of these muscles in the body wall. In addition to moving the animal, these muscles also produce a stiff tube which constitutes a "hydrostatic skeleton". There is no general theory for such a skeleton that would allow us to predict the shape of the animal's body from the activity pattern of its motor neurons. Therefore, the goal of this proposal is to use a combination of experimental measurements and numerical simulations to derive a quantitative description of hydrostatic skeletons in general and of the leech in particular. This study will proceed in three steps: 1. Describing leech movements in biomechanical terms. Segmental volumes, muscular tensions, geometric relationships of the muscles, internal pressures, and fluid flows will be determined. 2. Developing an analytical model of hydrodynamic skeletons. The current best model will be expanded to produce more realistic body forms, using the physical measurements obtained above. 3. Refining the model by comparing its performance to behaviors. Measurements during the production of simpler behaviors (bending and shortening) will be used to determine parameters which will tested by the model's ability to produce the more global behaviors (swimming and shortening). Such a model should be applicable to other hydroskeletons as well.***
