143] LIFE HISTORY OF GORDIUS AND PARAGORDIUS—MA Y 23 



is placed over the drop about half of the specimens will become active 

 within five or ten minutes. The reaction is not due to pressure as the 

 larvae can easily stand on end in the ordinary film of water. It may be a 

 reaction to the lack of oxygen or the presence of carbon dioxide in the 

 water. 



The larvae bore their way into any animal tissue that happens to be 

 accessible at the time. Villot was the first to discover this, and since he 

 regarded all these animals as true hosts of the parasite, he stated that 

 Gordius has no specific hosts. Later Villot himself, Montgomery and 

 others found that the larvae merely encyst in most of these animals and 

 are unable to undergo further development. 



PARASITISM 



With the entrance of the larva into the proper host begins one of the 

 most important phases of the life cycle, the period that leads thru growth 

 and differentiation to the formation of the mature worm. 



The final and perhaps the only hosts of Gordius robustus I have found 

 to be members of the grasshopper family Locustidae. The most common 

 host around Urbana is Orchelimum vulgare Harris, but Orchelimum nigripes 

 Scudder and Xiphidium nemorale Scudder seem to be equally heavily 

 infected tho less common, and I have obtained two adult parasites from a 

 female of Scudderia furcata Brunner. Over 100 specimens of Xiphidium 

 fasciatum (DeGeer) from localities in which Orchelimum vulgare was heavily 

 infected were examined but no infection was found. Over 200 specimens 

 each of Melanoplus diferentialis and Melanoplus femur-ruhrum from similar 

 localities also proved to be not infected. Large numbers of Gryllus assi- 

 milis and Nemobius fasciatus examined in the investigation on Paragordius 

 varius were also not infected with Gordius robustus. Many aquatic insect 

 larvae were also examined, but no infected specimens were found. From 

 two to three percent of the crickets and grasshoppers examined were found 

 to be infected with Mermithidae. 



An intermediate host is not necessary. If one occurs in nature it can 

 be nothing more than a carrier in which the larva undergoes no change. 

 Evidence presented later shows that a larva that has begun to change into 

 the parasitic form can not undergo a change of hosts without being destroy- 

 ed in the process. Furthermore, I have succeeded in producing in the 

 laboratory an infection of at least fifty per cent in Locustidae collected 

 in a locality in which later collections showed that no infection occurred 

 in nature. 



I 1. On July 6, 1916 forty-one young Locustidae, mostly Xiphidium 

 fasciatum and Orchelimum vulgare were infected by injecting a drop of water 

 in which larvae of Gordius robustus were suspended into the abdomen by 

 means of a capillary pipette made of hard glass. From counts made on 

 similar drops of the suspension placed on a slide under the microscope it 



