DIGESTION AND METABOLISM 



19 



sundry other minute animal forms, and these will all be ingested 

 adding their bulk to the food foraged on the surface of the ground. 

 A number of fresh- water oligochaetes e.g. Tubifex are also omni- 

 vorous in the muds of lake and river bottoms, though probably a 

 considerable proportion of their intake will be bacteria, since they 

 live in situations in which oxygen is often at a premium. A few 

 oligochaetes are carnivorous, consuming rotifers, fish, frogs, 

 flies and other worms (Stephenson, 1930), and the Branchiob- 

 dellidae are external parasites on crayfish. 



Species in which g.3 



enzymes named ;gi 



have been 2 i 



found <-^ 



Fig. 7. The alimentary canal, structure and enzyme secretions. 



The table shows the various regions and the segments in which 



they are found in Liimhricus, The functions of these areas, glands 



and pH are also indicated. 



In view of the catholic eating habits of most oligochaetes, as 

 outlined above, it is not perhaps surprising that in the few species 

 studied there are a wide range of enzymes present in the gut. 



Lesser and Taschenberg (1908) made extracts of the gut of 

 L. terrestris and incubated them with starch, glycogen, cellulose 

 and inulin. All these substances appeared to be attacked and broken 

 down. Another early study indicated that lichenin, obtained from 

 lichens, is hydrolysed. The enzyme was appropriately named 

 lichenase (Jewell and Lewis, 1918). 



