NO. 15 ARTHROPOD HOSTS OF HELMINTHS HALL 3 



enter a second intermediate host, an aquatic arthropod or a small fish, 

 and encyst in this host. When such a second intermediate host is 

 eaten by a primary host, the fluke develops to maturity in the new 

 host. 



Among the nematodes we have several groups which are usually 

 monoxenous, although some of the ascarids, belonging to a super- 

 family, the Ascaroidea, which is ordinarily monoxenous, may be 

 heteroxenous, as in the case of a seal ascarid having a larval stage 

 encysted in fish. One large and important group, the Filariata, 

 composed of two superfamilies, the Filarioidea and the Spiruroidea, 

 is a heteroxenous group with larvae developing in blood-sucking 

 arthropods or in arthropods which feed in some stage of development 

 on the feces of the primary host or on food contaminated with these 

 feces. 



Among the acanthocephalids we 'know of the occurrence of inter- 

 mediate hosts, but for the most part we must assume that this is the 

 rule, as very few life histories are known in this group. In the known 

 cases the worm eggs passing from the primary host infect secondary 

 hosts, develop to a larva and infect primary hosts when these eat 

 infected secondary hosts, or else re-encyst in another intermediate 

 host and infect the primary host when it eats the second intermediate 

 host. 



The lists of heteroxenous worms and their arthropod hosts, given 

 in this paper, are the most complete of those published and the omis- 

 sions are probably few. The lists for certain groups have been com- 

 piled from time to time, some of the more important and more recent 

 being those of Joyeux (1920), Ransom (1921), \'^an Zwaluwenburg 

 (1928), Seurat (1916, 1919), MacGregor (1917), and Henninger 

 (1928), and, of course, the indispensable catalogues of Stiles and 

 Hassall, but no previous paper has attempted to cover all the arthro- 

 pod hosts of the parasitic worms of vertebrates. On the basis of the 

 lists given here this paper includes a consideration of the general facts 

 and of the broad principles which may be derived from a correlation 

 of these facts. While it will serve as a reference for the trained 

 scientist in the groups involved, its principal value will be as a ref- 

 erence and guide to the younger worker and student and to the man 

 who works in places remote from adequate library facilities and the 

 specialized literature on arthropods or parasitic worms. The subject 

 of the paper excludes from consideration the worms which have 

 arthropods as primary hosts, and the arthropods which are inter- 

 mediate hosts for Protozoa or animal parasites other than the worm 



