Collagen of the Earthworms

The problem of the complex configuration of the collagen in the Oligochaeta has not yet been conclusively solved. Since the last century, evidence has been found of a fibrous structure lying above the epidermis (constituting the cuticle) and of another one lying below it (constituting the supporting structures). The cuticle, easily examined by physical and chemical methods, was analyzed minutely by Singleton (1) and by Maser and Rice (4), who found 80 % of it to be proteins (with a high content of hydroxyproline, glycine, and alanine), and 20% to be carbohydrates. These results, as well as the X-ray diffraction pattern, pointed to the presence of collagen. On the other hand, the fibrils observed in the electron microscope have never seemed to show a periodic structure (2-5). It is thought that the collagen molecule of Oligochaeta is twice the weight and length of that of the vertebrates, i.e. it is a dimer of tropocollagen (4). Although the presence of abundant subepidermal connective tissue in the Oligochaeta has been known since the works of Cerfontaine (6), Bock (7), Schneider (8), and Stephenson (9), no detailed description of it has been available until quite recently. It was only in 1961 that Ruska and Ruska (3) visualized in the electron microscope a 560 A cross-banding in the fibrils of the subepidermal layer of Lumbricus, and in 1962 that Van Gansen (10) observed fibrils with a 140 m period around the intestine and in the blood plexus of Eisenia. In earthworms, the external and internal collagens seem to differ in structure, and the question deserves further study. It is for this reason that I have examined the connective tissue of these animals by as many methods as possible.