538 



manual oP Elementary zoology 



Relations 

 between 

 Animals 

 based upon 

 Nutrition. 



stored by plants in the complex substances they manu- 

 facture. It is stored by plants : most of it is not set free till 

 it reaches the bodies of animals. There is, of course, no 

 circulation of energy. That which is set free from the 

 bodies of organisms is lost to them, and has to be replaced 



by the fixing of more 

 energy from the sun's 

 rays by plants when 

 they work up the ex- 

 creta of animals. 

 The whole animal 

 kingdom 

 may be 

 regarded 

 as a vast 

 complex 

 system which, by 

 means infinitely more 

 subtle than those 

 which are possible in 

 the organic realm, 

 disposes of the ma- 

 terial and energy ac- 

 cumulated by plants. 

 The relations be- 

 tween the different 

 kinds of animals are 

 based in the long- 

 run upon nutrition. 

 Either animals com- 

 Fig. 396.-A hermit crab withdrawn from pete for the common 

 its shell. The anterior legs are cut supply of food which 

 short.— From Thomson. is derived directly or 



hd., Head ; th., thorax ; aid., abdomen. indirectly from plants, 



or some of them serve 

 others for food, or in rarer cases they assist one another in 

 the quest for food or in defence against enemies which 

 would use them for food. We may class animals according 

 to their food as omnivorous, herbivorous, and carnivorous, 

 or according to their method of obtaining it as free living, 

 parasitic, symbiotic, and commensal. Most of these classes 



abci 



