114 RESPIRATION 



oxygen tension is almost nil, that they do not use oxygen at 

 all, in spite of which they produce considerable quantities of 

 carbon dioxide. Even when oxygen is offered them they are 

 unable to make use of it. On analysing such worms it has 

 been found that one-third of their dry substance is composed 

 of pure glycogen, and their energy — which of course is not 

 much, as they move but little and derive their temperature 

 from their host — is obtained by the breaking down of this 

 glycogen into carbon dioxide and certain fatty acids. Some- 

 what similar processes take place in earthworms and in certain 

 leeches, Clepsina and Nejphelis, when kept in an atmosphere 

 of pure nitrogen. Leeches will live in such an atmosphere from 

 two to six days. 



