1 1 76 BULLETIN OF THE BUREAU OF FISHERIES. 



A NEW TREMATODE PARASITE. 



Every one of the 7 fish examined contained specimens of a new trematode, 

 which I have named Azygia sebago. It is relatively insignificant in size and 

 difficult to detect amid the thick white mucus which lines the wall of stomach 

 and cEsophagus. Not a single host was without this parasite, and several salmon 

 sheltered considerable numbers ; yet in most cases they were not seen in life, but 

 only appeared after the stomach and its contents had been agitated in a pre- 

 serving fluid. Careful examination of the debris then never failed to disclose 

 some specimens of this worm. Moreover, it was the only species of trematode 

 that was found in the Sebago salmon. The description of the species may 

 properly precede a discussion of its biological characteristics. 



The genus Azygia was established by Looss (1899, p. 569) to include a well- 

 known European species, Distomum tereticolle Rudolphi, which was made the type 

 of the new genus. It was also the only species in the genus ; for, as Looss remarks, 

 he had not been successful in finding among the flukes that he knew any form 

 which could be included naturally with the old species, Distomum tereticolle. 

 There are at the disposal of the student several good descriptions and delinea- 

 tions of the old species, Azygia tereticollis Rudolphi, so that it is possible to 

 determine with precision its structural features ; the best of these descriptions is 

 undoubtedly that by Looss (1894). 



The new species, Azygia sebago,"' is much smaller than the older form, 

 measuring 10 mm. in maximum length and averaging 5 to 6, or less often 8 mm., 

 in well-developed specimens. Fortunately, I have a large range of sizes, from 

 such as are only barely over i mm. in length to the maximum noted, so that it 

 was possible to follow the changes accompanying the assumption of the adult 

 form. Specimens 2.85 mm. long have not yet produced ova. 



The general form of the body is cylindrical, bluntly rounded at the anterior 

 end, and tapering slightly toward the posterior end, which, however, is ulti- 

 mately rounded off. The body is regularly divided into two regions by a shal- 

 low furrow at which the direction of the long axis changes more or less (fig. 1), 

 giving the worm in lateral aspect much the appearance of a can-top tightener. 

 While the relation of the regions is very variable, at times forming almost a sin- 

 gle straight line and again standing at a considerable angle with each other, yet 

 one can make out these conditions even in specimens which are poorly killed and 

 badly distorted. The anterior region assumes the form of an elUpse surrounding 

 the two suckers. This region changes relatively little in size with growth. In 

 one of the smallest specimens measured (1.6 mm.) the distance between the 



a During the spring of 1908 two of my students, Messrs. W. N. Anderson and H. B. Boyden, made 

 a study of this form and prepared a partial report on its structure, to which I am indebted for some 

 of the data in the following description, and also for two figures. 



