ZOOLOGY, ENTOMOLOGY, AND MEDICINE 223 



OBSERVATIONS ON SEASONAL DISTRIBUTION 



AND LONGEVITY OF SOME ACANTHO- 



CEPHALA FROM FRESH-WATER HOSTS 



ABSTRACT 



H. J. Van Cleave, University of Illinois 



In collecting fresh-water Acanthocephala the writer has 

 been impressed by the varying degrees of infestation of cer- 

 tain vertebrate hosts at different times of the year. A search 

 of the literature has furnished no accurate information on this 

 subject, so it seemed worth while to investigate the question, 

 especially since Linton in a recent paper has rather summarily 

 dismissed the topic with a brief generalization. Records of 

 the occurence of three species belonging to the genus Neo- 

 echinorhynchus have been studied with the following results : 



1. Seasonal distribution of fresh- water Acanthocephala 

 varies in different species. No general statement can be made 

 to apply to the entire group. 



2. N. emydis occurs in turtles from some localities at all 

 seasons of the year. The same individual host bears a mixture 

 of mature and immature parasites. This indicates that the host 

 is constantly exposed to sources of infestation. There is no 

 cyclic change in the degree of infestation from month to 

 month. 



3. N. gracilisentis enters the intestine of the gizzard-shad 

 in early fall and continues to develop until April or May, 

 when it attains sexual maturity and is finally expelled. Dur- 

 ing the summer months the host is not parasitized by this 

 species. 



4. iV. longirostris infests the intestine of the gizzard-shad 

 in the summer, reaches full sexual maturity in mid-winter, and 

 disappears entirely in spring and early summer. 



5. The demonstrable presence of a seasonal cycle in the 

 life history of a parasite involving two or more hosts is de- 

 pendent upon: (a) longevity of the parasite in the final host; 

 (b) extent of the time in which infestation of the final host 



