BIOCHEMICAL ARCHITECTURE 13 



reference to the long axis which itself lies in the plane of the cuticle. 

 Millard and Rudall (1960) have shown that the deepest regions of 

 the cuticle, nearest the secreting epithelial cells, are probably areas 

 in which the filaments are still growing. In the outermost layers 

 there is a sudden decrease in size of filaments as if their substance 

 was being resorbed. "Papillae" arising from the surface of the 

 epithelial cells contain tube-like prolongations of the cell interior 

 passing out to the plasma membrane. These may be the points of 

 secretion of the cuticular filament substance. 



The collagenous nature of the earthworm cuticle has been 

 confirmed many times since (Rudall, 1955; Watson and Smith, 

 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 counter- 

 part. There is no trace of hydroxy lysine 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 



