Occasional Papers of the Museum of Zoology 5 



A', crassus, is yet unknown for any other host as well as 

 from any other locality. The diversity of its acanthocephalan 

 infestation offers a number of interesting biological problems 

 for consideration. Conditions for existence for the sucker 

 are apparently not very favorable in Douglas Lake. This is 

 probably one of the reasons for the great diversity in infesta- 

 tion. Professor Reighard (1915:225) has called attention to 

 the large numbers of dead suckers that are thrown upon the 

 beach during the summer. According to his observations they 

 present strong evidence of starvation for they do not seem 

 to be diseased "and are not usually parasitized heavily enough 

 to account for their emaciation." If lack of proper quantities 

 of suitable food may cause the death of numbers of individuals 

 of this species it is not an unwarranted assumption that many 

 individuals are led to take as food, organisms which under 

 normal conditions are not included in the diet of members of 

 this species. In this manner parasites not normally found in 

 the digestive tract of this species find entrance with the unus- 

 ual food substances taken by the starving fish. It is apparent 

 that the primary or intermediate host of Echinorhyuclius tlic- 

 catus cannot normally serve as any conspicuous portion of the 

 food supply of the sucker, for at tlie season when other species 

 of fishes in the same locality are carrying heavy infestations 

 of this parasite but one individual of C. comniersonii carried 

 a light infestation of this species. Its entrance into the intes- 

 tine must have been due to some unusual circumstance such as 

 that mentioned above. 



La Rue's field notes show that of the fifteen specimens ex- 

 amined only seven were adult. Of these adult specimens only 

 one was free from infestation and the epithelium lining the 

 intestine of this one showed thickened patches surrounding 

 pits which were evidently the scars left by the removal of pro- 



