ARTHROPODS AS INTERMEDIATE HOSTS OF 

 HELMINTHS 



By MAURICE C. HALL, 



CHIEF, ZOOLOGICAL DIVISION, BUREAU OF ANIMAL INDUSTRY, 

 U. S. DEPARTMENT OF AGRICULTURE 



INTRODUCTION 



The phylum Arthropoda contains numerous forms which serve as 

 intermediate hosts of many parasitic worms, including nematodes, 

 acanthocephalids, flukes, and tapeworms. This fact follows naturally 

 from the fact that the arthropods are an exceedingly large group of 

 animals, including the ubiquitous insects and the numerous and widely 

 distributed crustaceans. It also follows from the fact that these arthro- 

 pods constitute the food supply, wholly or in part, for so many higher 

 animals, especially for such forms as fish, many amphibians, some 

 reptiles, numerous birds, and some mammals. To a lesser extent it 

 follows from the fact that in feeding on various plants the higher 

 animals are certain to swallow the arthropods habitually present on or 

 in these plants. It follows from the fact that many insects feed on or 

 breed in manure and consequently are exposed to infection from the 

 eggs or larvae of worms parasitic in the hosts responsible for the 

 manure. Last, but not least, the importance of arthropods as inter- 

 mediate hosts of parasitic worms follows from the fact that large 

 numbers of anthropods, especially the innumerable biting insects, 

 whether transient or permanent ectoparasites, feed on blood and so 

 serve as intermediate hosts of worms which have larval stages living 

 in the blood of vertebrates. 



The worm parasites may be classified from one point of view as 

 monoxenous or heteroxenous. The monoxenous worms have life 

 histories in which the worms pass from one host animal to a similar 

 host animal without the intervention of an intermediate host. The 

 heteroxenous worms have life histories in which in most cases the 

 worms pass from mature stages in one host animal to larval stages in a 

 host animal of a dififerent sort, the intermediate host, and then return 

 to a host animal of the first sort or a more or less closely related 

 species and develop in this animal to maturity. In some instances two 

 intermediate hosts are utilized in sequence for larval stages. 



Smithsonian Miscellaneous Collections, Vol. 81, No. 15 (End of Volume) 



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