498 GENERAL CONSIDERATIONS 



parasitism are afforded by lice which resort to the body of the host for 

 but a brief time, as in the case of some hce which hve in poultry houses 

 and go upon the poultry for only a short time at night to feed; other 

 examples are mosquitoes, sucking flies, leeches, and ticks, which are on 

 the host only long enough to fill themselves with blood. Permanent 

 parasites (Fig. 308) are such as the ascaris, which enters the body of 

 the host in the form of an embryo within the egg and remains in that host 

 throughout life. Parasitism may not involve intimate bodily contact at 

 all, such as in the case of some ants which live a life of piracy in the hills 

 of other ants larger in size. The parasites make small tunnels which 

 open into the larger ones of the host ants. The former get their living 

 by stealing food from their hosts, which are unable to follow them into 

 the small tunnels to regain it. 



566. Predatism. — Parasitism may in the end lead to the death of the 

 host. This is not, however, to the interest of the parasite, which finds 

 ease and safety in the relationship. If the death of the host does follow 

 immediately after one animal attacks another, then the association is of 

 the nature of predatism rather than parasitism, predatism being the eating 

 up of one animal by another. Predatism is exhibited typically by those 

 animals which we term predatory and which feed upon other animals by 

 killing and devouring them. While the relationship of symbiosis is 

 often considered as existing between animal and plant organisms and 

 while that of parasitism may involve plants parasitic upon animals, the 

 term parasitism is not often applied to animals living on plants as do 

 lice or mites, nor predatism to the eating of a plant by an animal. So 

 generally do plants form the food of animals that to recognize these as 

 involving either parasitism or predatism would make the terms of dis- 

 tinctly less value. 



