1198 BULLETIN OF THE BUREAU OF FISHERIES. 



The method employed in the examination of the flesh for parasites was the 

 same I have used in examining butterfish in previous years. The fish were 

 spHt open longitudinally and the flesh separated from the backbone and verte- 

 bral spines. Occasionally the flesh was further divided. This method exposes 

 the usual location of flesh parasites. 



PRINCIPLES OF DISTRIBUTION OF ENTOZOA. 



In order that the subject-matter of this paper be perfectly clear, it is neces- 

 sary to give a brief resume of the principles which determine the distribution 

 of the entozoa. The term "entozoan' ' is a convenient general designation for any 

 animal which lives within another animal. The adult egg-producing animal lives 

 in the alimentary tract, or some part in direct connection with the alimentary 

 tract, as the bile duct, or, in the case of air-breathing animals, also in the air 

 passages. As a rule the eggs, or in the case of the cestode or tapeworm the 

 ripe joints, which separate from the parent chain, are thrown off' with the natural 

 discharges of the animal in which they are living. The animal which harbors 

 the adult tapeworm is called the final host. In order to develop, the eggs, as 

 a rule, must enter the alimentary tract of another animal. In this animal the 

 eggshell is digested off and the minute embryo thus liberated penetrates the 

 mucous membrane of this second or intermediate host and sooner or later comes 

 to rest. A cyst of connective tissue is formed around it by the tissues of its 

 host. In this cyst the parasite remains quiescent, and ordinarily this is the 

 end of the individual unless it is swallowed by the animal in whose alimentary 

 canal it can become sexually mature. In this case another generation of eggs 

 is produced and the round of life from egg to egg again is completed. 



In the majority of instances a cestode egg gives rise to but one adult chain. 

 In a few instances a large number may develop from one egg, on account of 

 the multiplication of larvae by a kind of budding in the encysted stage. So 

 far as I have observed, there are no examples of this latter method of repro- 

 duction among the cestodes that infest fishes. 



ZOOLOGICAL ORDERS REPRESENTED BY FLESH PARASITES OF FISHES. 



The following groups are represented in the parasites which I have found in 

 the flesh of our marine food fish: 



SPOROZOA. 



These protozoan parasites occur in small white cysts, usually along the 

 backbone of small fishes. They seem to be of rather common occurrence in 

 young alewives and herring." I have not examined many full-grown herring 



"Linton, E.: Parasites of fishes of the Woods Hole region. Bulletin U. S. Fish Comniission, vol. 

 XIX, 1899, p. 438, 439. 



