Embolic coils with detachable segments that are separated by detachment capsules that are thermolytically degradable such that varying lengths of coil may be implanted into a vascular malformation to occlude same. The capsules are radiotransparent when compared to the adjoining coil segments to the location of the segments is easily seen. The capsules further include protruding electrical contacts that make positive contact with terminals on a delivery catheter. The terminals on the delivery catheter serve as markers so the relationship between the detachment capsules and the terminals is easily visible under x-ray.