PARASITIC ROUND WORMS 537 



beetles, grasshoppers, and crickets, are found well-grown and nearly 

 mature larvae of the hairworms. On escaping into the water from 

 these insects, the worms become sexually mature and the cycle is 

 completed. Villot denied the necessity of an intermediate host, 

 but others have held that the hairworm undergoes two and per- 

 haps more changes of host during the complete life cycle. When 

 the worm escapes from an insect it swims about actively in the 

 water but even where the capillary esophagus is not closed so that 

 the taking of food is absolutely precluded, the worms probably 

 take no nourishment in the aquatic stage. 



Hairworms in an early or late larval condition have been re- 

 corded as parasites not only in the insects cited above but also less 

 frequently in spiders, oligochaetes (Lumbriculus) , snails, and rarely 

 in distomes, fish, and amphibians (?). In the last three types their 

 presence is no doubt purely accidental. Adults in the free-living 

 stage have been reported a number of times as human parasites. 

 Here their presence is also fortuitous and is doubtless due to the ac- 

 cidental swallowing of specimens in water or in food eaten uncooked. 



The number of species of Gordiacea in North America is not 

 large and thanks to the splendid work of Montgomery the group 

 is well known. The following synopsis is based on his papers. 

 The range of species has been somewhat increased by my own col- 

 lections from regions not represented in his records. I have also 

 been given valuable unpublished data by H. G. May. Even yet 

 there are no records from the southeastern or northwestern United 

 States and only a single record each from Canada and Alaska. 

 The absence of records from any region indicates lack of study in 

 that region rather than scarcity of material. 



Only three well-marked genera are known: Gordius, Chordodes, 

 and Paragordius, all of which are represented in this continent. 



KEY TO NORTH AMERICAN GORDIACEA 



i (8) Anterior region distinctly attenuated, coming nearly to a point; usu- 

 ally lighter than the rest of the body and without a dark 

 ring Chordodes Creplin 1847 . . 2 



Caudal end simple, not lobed; in female somewhat enlarged. External surface complicated; 

 several types of areoles present. 



Because the males and females are distinctly unlike in external appearance they come out as 

 separate groups in the key. The cross references carry the student back to the other sex in 

 each case. It will be noted that the key line which ultimately determines the species is usually 

 alike in both sexes. 



