8 PARASITES OF THE DOMESTIC ANIMALS 



Zobparasites are parasites which belong with the animal kingdom. 



Optional Occasional Parasites are those which only fleetingly visit 

 their hosts to obtain nourishment, but are not dependent upon them for 

 either nourishment or shelter. Example, mosquitoes. 



Obligate Occasional Parasites are those which do not permanently 

 live upon their hosts, but are dependent upon them for nourishment and 

 to some extent for shelter. Examples, fleas, bedbugs. 



Determinate Transitory Parasites are those in which the parasitism 

 is limited to a definite phase or phases in their life history, during which 

 time the parasitism is obligate and continuous. Examples, botflies, 

 ticks. 



Permanent Parasites are those in which the parasitism extends from 

 the hatching of the egg to the stage of reproduction in the adult. Exam- 

 ples, lice, many entozoa. 



Fixed Parasites are those which cannot pass spontaneously from 

 one host to another. Examples, larvse of botflies, Linguatula, helmin- 

 thes. 



Erratic Parasites are those which in their adult state may pass 

 readily from one host to another of the same or different and widely 

 separated species. Examples, mosquitoes, biting flies, ticks, leeches. 



Determinate Erratic Parasites are those which may pass from one 

 host to another of the same species, or a species closely allied to the one 

 abandoned. Examples, lice, psoric Acarina. 



Monoxenous Parasites are (a) those the eggs of which are expelled 

 by the host, the embr3'^os, while still within the eggs, passing to a new 

 host where hatching and development to the adult occurs. Example, 

 Ascaris. 



(b) The eggs having been hatched, the larvae are nourished in suitable 

 conditions of moisture and temperature, but cannot undergo further 

 development until they have reached the body of their host. Example, 

 Hemonchus contortus. 



Heteroxenous Parasites are (a) those which pass to their definitive 

 host by an intermediate or transitory host, in which they cannot attain 

 their complete development; consequently, a reciprocal transmission 

 between these hosts is essential to the development and propagation of 

 the parasite. Examples, tapeworms, Plasmodium of malaria. 



(b) The eggs of the parasite are hatched in the body of the host, the 

 embryos invading the tissues of the same individual host and not at- 

 taining the adult state until they have reached a second host. Example, 

 Trichinella spiralis. 



Transmigration is a term applied to the passing of heteroxenous 

 parasites from one host to another. 



Incidental or Stray Parasites are those which under natural condi- 

 tions are occasionally found in unusual hosts. Examples, Gigantorhyn- 



