Complex systems of tubules, 30-40 nm in diameter, were observed in myofibers of the soleus muscle of Wistar rats following experimental transection of the Achilles tendon. The appearance of these systems varied remarkably, depending upon the plane of sectioning. The spacial arrangement of the tubules was reconstructed by comparing several sections through individual systems. Such reconstructions revealed that they are networks of tubular elements arranged in an hexagonal pattern. A three-dimensional wire model was prepared, illustrating the spatial organization of the tubular systems. The model consists of four groups of lattices with a honeycomb-like arrangement. The lattices of each group are parallel to one another, and intersect those of the other groups at an inclination of 60 degrees.