1956; Watson, 1958), but there is at least one important diflference compared with vertebrate collagen : there is no periodicity of the fibrils at 640 A intervals in either L. terrestrts (Watson and Silvester, 1959), or A. longa (Reed and Rudall, 1948) (Fig. 5). The cuticle is highly proteinaceous in character, some 80% of the total being composed of protein whilst the remaining 20% is made up of polysaccharides, galactose, pentoses and hexosamines (Watson, 1958). Nitrogen accounts for 14-6% of the cuticle weight and at least 16 amino-acids are represented in the protein. The amino-acids of the cuticle of two species, L. terrestrts and A. longa are Hsted in Table 3 where they are compared with a typical vertebrate collagen, that of ox-hide (Watson and Smith, 1956; Watson, 1958; and Singleton, 1957). Amines with non-polar side chains e.g. glycine, are present in quantities similar to those in vertebrate collagen, but arginine, histidine, and lysine with basic side chains are less abundant than in vertebrate material, whilst aspartic acid, glutamic acid and serine (D-serine?) with acidic side chains are present in greater quantities than in the vertebrate counterpart. There is no trace of hydroxylysine in earthworm cuticle. The gizzard of L. terrestrts is lined with a cuticle. This can be removed and Rudall (1955) subjected this material to X-ray analysis, obtaining patterns similar to those of chaetae (see p. 15). Cuticle from this situation is not stable in hot dilute alkali, does not crystallize, and though chitin-like is not in the a-chitin form. The presence of a chitin would be shown by a fibrillar structure, but van Gansen (1959b, 1960) using similar material finds no evidence for the belief that the gizzard lining is fibrillar. Chemical tests with orcein, resorcin, van Gieson stain, benzidine and Gomori stain