28 ILLINOIS BIOLOGICAL MONOGRAPHS (148 



that the earlier collections of 1914 did not show the difference in infection 

 between males and females that was noticed later. Whether the later 

 difference is due to the fact that infected males die early or to the fact that 

 males mature and lose their parasites earlier than do the females has not 

 been determined. 



No actual observations on the length of the parasitic period have been 

 made, and since the data bearing on this subject are given elsewhere, this 

 topic may be left for later discussion. 



The period during which parasites become mature and emerge from 

 their hosts lasts from early September until late October. In 1914 no 

 collections were made before September 21 and only a few hosts were 

 collected before September 23. On the latter date 78 hosts were collected 

 and several parasites escaped before the collection was brought to the 

 laboratory. The first large collection in 1916 was made on September 5 

 and jdelded 64 parasites of which three were developing the brown color. 

 Of 8 parasites obtained on September 6 one was developing color, 20 obtain- 

 ed September 7 were all white, but 80 collected September 8 included 5 

 adults ready to emerge. The other limit to the time for emergence is set 

 by the death of the last host. In 1914 the last big collection containing 

 126 hosts, was made on October 3 and yielded 17 parasites. The record 

 contains a note stating that one of the specimens was the youngest obtained 

 to that time and that the material should be good for study as it contained 

 specimens of all ages. After that Orchelimum vulgar e became more and 

 more scarce. On October 17, 54 hosts were collected and were found to 

 contain mostly mature parasites, but a few that were not fully developed. 

 In three further collections made respectively on October 24, 29, and 31, 

 only that of October 29 contained a single female of Orchelimum vulgare. In 

 1916 the latest collection was made on October 14 and according to the 

 records one parasite was still quite young. At that time the hosts were so 

 extremely scarce that no further collections were made. 



Without exception I have found the parasites escaping with the an- 

 terior end first from a region near the anus of the host. In all I have seen 

 more than two dozen specimens of Gordius robustus escape from their hosts. 



The mature parasites in the hosts react definitely and quickly to water. 

 On September 24, 1914 one specimen of Orchelimum vulgare when caught 

 was found to have the anterior end of a Gordius protruded at its posterior 

 end. When the host was dropped into the bottle and thus the pressure on 

 the abdomen released the parasite withdrew. After a short time the bottle 

 was partly filled with water and the parasite emerged within one minute. 

 On the same date two other hosts with parasites in the same stage were 

 collected and placed in a dry bottle. During the remainder of the trip 

 which lasted about two more hours the parasites remained in the hosts. In 

 the laboratory the hosts were placed in water and in about one minute the 



