1 I So BULLETIN OF THE BUREAU OF FISHERIES. 



dorso - ventral or oblique fibers which are not subject to any regularity in 

 arrangement. These are longitudinal fibers extending from the oral sucker 

 throughout the entire length of the distome, as is clearly seen in a frontal section 

 (fig. 4, pi. cxxi). In position they lie one-fourth to one-fifth the radius of the 

 section distant from the external surface. The cross sections of these fibers 

 show them to be much heavier than the other muscle elements and to occupy 

 an oval zone parallel to the outer surface of the body. They divide the body 

 accordingly into a cortical and a medullary portion. The vitellaria are the only 

 conspicuous organs which lie in the cortical layer. This muscle layer is 

 undoubtedly related to the marked contractions of the fluke which have already 

 been commented upon. Unfortunately I have no material available from 

 which to determine whether similar fibers also exist in .4. tereticollis.- Looss 

 (1904) does not mention them. 



The relations of oral sucker, pharynx, and crura, the convolutions of the 

 intestinal branches, the coils of Laurer's canal and of various ducts and the 

 sinuous course of the collecting tubes in the excretory system all point toward 

 the variable extensibility of the worm. Differences in caliber and in the dis- 

 tance between organs also indicate the sanie. Observations on the living 

 parasite serA'e to show that it is constantly extending and contracting the body 

 to such an extent as to double or halve the length within a few seconds of time. 

 In fact, I have never before observed a form which indulged in such energetic 

 twisting and contracting. This habit renders any observations on the living 

 worm very difficult. 



Looss (1894, p. 7) comments on the active migration of A. tereticollis after 

 the death of the host, a feature previously recorded for D. cylindraceum by 

 Braun (1890, p. 568). A. sebago manifests the same tendency in the most 

 marked degree. The normal seat of this parasite I feel sure is the stomach, 

 and perhaps the oesophagus also, but even a slight delay in the examination of 

 the host resulted in finding single specimens well down the intestine as well as 

 up in the pharynx and even among the gill filaments. In one case a salmon 

 caught late in the day was kept overnight to be photographed, as it was a 

 peculiarly fine specimen. When the viscera were examined, about twenty 

 hours after the capture of the fish, my field notes record that there were 36 dis- 

 tomes in the air bladder and that they were seen coming in through the ostium 

 with mucus from the cesophagus. Other specimens were found in the pharynx 

 and gill cavity and one even in the body cavity. The last can be attributed 

 no doubt to some tear in the alimentary lining which permitted the fluke to 

 make its way unhindered into what is ordinarily a closed cavity. In still 

 another salmon which had gorged itself on smelts my field notes contain com- 



