277] NORTH AMERICAN MONOSTOMES 59 



While this species was reported by MacCallum as "not by any means a 

 constant parasite," he having found it in only one host infected of a number 

 examined, more recent data show this worm to be rather constantly present. 

 In seven specimens of Chrysemys marginata collected in the summer of 1911 

 from Lake Emily, Minn., Barker and Parsons found five infected, one of 

 them yielding thirteen worms from both lungs. The same authors (1917) 

 found that female turtles were more than three times as heavily infected 

 as males, Stunkard (1919) from the examination of "about three hundred 

 turtles" reports the heaviest infection in one host as six. On an examina- 

 tion of "more than fifty turtles" he found no difference in the relative in- 

 fections of males and females. The writer has examined one hundred and 

 two hosts of six different species and of these forty-four showed infection 

 with these worms. The highest percentage of infection for any species was 

 found in Cinosternum pennsylvanicum from North Carolina in which 34 

 out of 45 specimens or approximately 75 percent were infected. The highest 

 number of individuals from a single host of this species was eleven while a 

 single individual of Graptemys geographicus, and the only one of eighteen 

 which showed infection, carried twelve worms in both lungs. 



During the past four years the writer has had opportunity to examine 

 more than one-hundred turtles as stated above. It was noted early in the 

 investigation that the collections made in different seasons showed no 

 striking difference in percentage of infection. It was then undertaken to 

 determine if possible the length of life of this parasite in the definite host. 

 It is generally understood that most intestinal paraties have an annual 

 cycle and depend on this for continuity of the species. However, data on 

 this point seems lacking in this group. The work on Heronimus chelydrae 

 consisted in the examination of a number of turtles collected in the same 

 region, Raleigh, North Carolina, at various seasons of the year. 



Some of these dissected on arrival showed relatively heavy infections, 

 others which were kept in the laboratory aquaria for periods of six, twelve 

 and eighteen months still carried infection, and a single specimen of Chely- 

 dra serpentina which had been kept in an aquarium for more than three 

 years yielded two specimens of Heronimus chelydrae and a single nematode, 

 probably Camallanus americanus. As was stated above hosts examined 

 when taken, usually carry intestinal forms in addition to the lung fluke 

 already mentioned, while those which have been kept in aquaria for a 

 period of six months or more show a marked reduction in the number of 

 the intestinal forms. There is no apparent change in the number of the lung 

 flukes present. 



Little is known regarding the condition of parasites during hibernation 

 of the host. Blanchard (1903) records that hibernating marmots do not 

 contain any intestinal parasites. Ward (1909) reports observations carried 

 out on the frog, Rana virescens. In this he says that parasitic infection 

 increases steadily up to hibernation, and does not decrease during the latter 



