152 ILLINOIS ACADEMY OF SCIENCE 



metabolic processes are present at any stage in the develop- 

 ment of the individuals. They are parasitic throughout 

 their existence. They reach maturity in the digestive tract 

 of various vertebrates. Eggs enclosing the developing 

 young are discharged with the feces of the vertebrate host. 

 These embryos never are freed from their shells until they 

 are taken into the body of some suitable primary host 

 (usually an arthropod) in whose body they can undergo 

 their development up to a certain stage. They never reach 

 sexual maturity and have no power of reproduction within 

 the body of the primary host. Development to maturity is 

 possible onl}' under condition that the primary host is 

 eaten by a suitable vertebrate in whose intestine the liber- 

 ated larva finds shelter and an abundant food supply to 

 bring it to the close of its life cycle. The absolute depend- 

 ence of the Acanthocephala upon some other organism 

 throughout their entire development renders a knowledge 

 of them of prime importance in the study of hosts which 

 harbor them. 



The effect of these parasites upon the fishes may assume 

 several different aspects. If present in large numbers in 

 a single host these worms appropriate elaborated food ma- 

 terial which should be utilized by the host, thereby reduc- 

 ing the available food suppl}^ for the host. Frequently they 

 are present in such large numbers that they fill the entire 

 cavity of the alimentary canal, thereby also interfering 

 with the digestive process. Another type of injury is that 

 due to the action of the proboscis in its normal functioning 

 as a holdfast organ. The proboscis is covered with hooks 

 or spines which penetrate the liningof the alimentary canal 

 of the host, thereby allowing the parasite to maintain its 

 position against the peristaltic movements of the intestine. 

 These minute spines cause lacerations and in some cases 

 perforations of the intestine through which disease produc- 

 ing organisms find access to the blood system and to the 

 body cavity of the host. Infections which under normal 

 conditions are resisted b}^ the unbroken mucosa of the 

 intestine are therebj'^ facilitated. For the reasons cited 

 above a study of these parasites is desirable because of 

 their direct or indirect effect upon fishes which have com- 

 mercial value. 



