78 Roosevelt Wild Life Bulletin 



has acquired entirely new hosts through its larvae becoming estab- 

 lished in unusual primary hosts that do not enter into the food supply 

 of the host of the mature worm. If the parasite were carried by 

 the migration of its usual normal definitive host into a locality where 

 the larvae failed to find their accustomed primary hosts, the larvae 

 might become adapted to entirely new species of animals in that 

 capacity. If these new species of primary hosts do not enter into the 

 food supply of the unusual definitive host the latter would thereby 

 become freed of the parasite in the newly invaded territory, and the 

 parasite might at the same time acquire as definitive hosts other 

 species which feed upon the newly gained primary host. 



DISCUSSION OF SPECIES 



But three species of Acanthocephala were encountered in the col- 

 lections from Oneida Lake, yet in the case of each of these distinctly 

 new biological data have been added. New host species are 

 added to those previously recorded for each of the three species: 

 Echinorhynchus thecatus Linton, Neoechinorhynchus cylindratus 

 (Van C), and Pomphorhynchus hulhocolli Linkins (in Van Cleave, 

 '19). For the last mentioned species an unusual host, due probably 

 to an accidental infestation, is also recorded. 



Echinorhynchus thecatus Linton, 1891. 



Length : females 11 to 26 mm. ; males 7 to 12 mm. Proboscis 

 usually about i mm. long. Neck about one-fourth the length of the 

 proboscis. Proboscis receptacle long and slender, about 1.5 times 

 the length of proboscis. Central nervous system near center of 

 receptacle. ' Proboscis hooks arranged in 12 longitudinal rows of 

 12 or 13 hooks each, adjacent rows alternating. Each hook 

 ensheathed in a cuticular collar. Embryos within body cavity of 

 gravid female 80 to iio/a long by 24 to 30/x wide. 



This species was by far the most abundantly represented of the 

 acanthocephalans in the fishes of Oneida Lake, having been taken 

 from the digestive tract of six of the nine species which were found 

 parasitized with these worms ; for three of these hosts there is no 

 previously published record of the occurrance of this parasite. These 

 new hosts for E. thecatus are : the eel (Anguilla rostrata), pike perch 

 {Stizostedion vitreum), and the chain pickerel (Esox reticulatu^) . 

 The obvious lack of specificity of hosts of this species renders it 

 capable of existence in numerous species of fresh- water and migra- 

 tory fishes. Many of the records of its occurrence are doubtless due 

 to accidental introduction into unusual hosts where it maintains itself 

 for a time without being able to reach sexual maturity. 



In the report on the Acanthocephala from fishes of Douglas Lake, 

 Michigan, I called attention ('19a, p. 6) to the fact that the small- 

 mouthed black bass (Micropterus doloinieu) is preeminently the 

 definitive host of E. thecatus in that region. The same intimate 



