46 



ZOOLOGY. 



and around it they are ectoplastic. A greater degree of 

 katabolism usually accompanies the formation of those 

 secretions (like the digestive juices) which are useful to the 

 animal but do not form part of its tissues. The greatest 

 amount of katabolism generally results in the production of 

 those useless or waste compounds, the excretions (chap, i., 

 13). These statements must not, however, be taken as 

 rigid and without exception ; they merely express a rough 

 general rule, which may be put in diagram form thus : 



: PKOTOPLASM 



Food-Material. 



Plastic Products 



Useful Secretions. 



Excretions. 



