The two nerve-rings are connected by fibres passing from one to the other.
This is the typical arrangement, which is exhibited in the majority of the Polychaeta and Oligochaeta; in these the successive chambers of the coelom are separated by the intersegmental septa, sheets of muscle fibres extending from the body wall to the gut and thus forming partitions across the body.
It is made by dusting on a specially prepared adhesive surface finely powdered fibres of cotton or silk.
The muscle-fibres arise as processes from the bases of the epithelial cells; such cells may individually become sub-epithelial in position, as in the polyp; or, in places where muscular tissue is greatly developed, as in the velum or sub-umbrella, the entire muscular epithelium may be thrown into folds in order to increase its surface, so that a deeper sub-epithelial muscular layer becomes separated completely from a more superficial bodyepithelium.
In the leaf-blade this sometimes aopears as a layer of thickened subepidermal cells, tht hypoderm, often also as subepidermal bundles of sclerenchymatou~ fibres, or as similar bundles extending right across the leaf from mu epidermis to the other and thus acting as struts.