526 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. 366) are such as the ascaris, which enters the host in 

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

 life. 



568. 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. Predatory animals feed upon other 

 animals by killing and devouring them. Unlike parasites they are thus 

 more powerful and usually larger than their victims. Predatism is the 

 term applied to such a relationship. Most relationships among organ- 

 isms may exist between animal and plant organisms but predatism is 

 not applied to the eating of a plant by an animal. 



