6 THE PHYSIOLOGY OF EARTHWORMS 



primitive oligochaetes Aeolosoma hemprichi and A. variegatum. 

 Eleven amino-acids have been identified in hydrolysates of both 

 these species: ten are common to both species, alanine, aspartic 

 acid, glutamic acid, glycine, leucine (or iso-leucine), lysine, 

 proline, serine, tyrosine and valine. In addition threonine is found 

 only in A. variegatum and methionine only in A. hemprichi 

 (Auclair, Herlant-Meewis and Demers, 1951). 



Muscles and Myosin 



The hydrolysis of the whole body, as in ^. hemprichi^ or of the 

 body wall musculature as performed by Thoai and Robin (1954) 

 breaks down the component structure of the tissues. In particular it 

 destroys the continuity of the muscle tissues converting protein 

 into the constituent amino-acids. 



The muscle layers of the body wall of L. terrestris are composed 

 of smooth fibres that lack the striations of typical vertebrate 

 skeletal muscle, but nevertheless have cross stripes. The individual 

 fibres have the shape of a ribbon with tapered ends. The width of 

 the ribbon is about 20 fi and the thickness between 2 and 5 ijl. 

 The contractile part of the fibre is covered with a thin layer of 

 undifterentiated sarcoplasm to which the mitochondria are confined, 

 and which contains a single nucleus. The fibrils, lying with one 

 edge at the surface of the fibre, and the other towards the interior, 

 are also ribbon-shaped. When the fibre is viewed in plan the two 

 sets of fibrils, one on either side of the ribbon, are found to show 

 an angle between them, never being parallel, and the value of 

 this changes depending upon whether or not the fibre is contracted 

 (Fig. \a). 



The fibrils show the same structure along their length but no A 

 or I bands are differentiated. There are conspicuous fixlaments 

 lying parallel with the long axis of the fibre, and there are approxi- 

 mately 100 filaments in a typical cross-section through a fibre. 

 They appear solid and circular in cross-section with diameters 

 ranging from 120-300 A. 



Between the fibres other structures are found. Each fibril bears 

 stripes upon one surface and bridges external from the stripes to 

 the adjacent fibril, but the bridges do not connect stripe to stripe, 

 rather they connect stripe to the stripeless surface of the next 

 fibril (Fig. lb, Hanson, 1957). Hanson and Lowy (1960) indicate 



