INTERNAL PARASITES OF THE SEBAGO SALMON. 1 1 79 



stress was originally laid on the extent of the vitellaria. The condition of the 

 vitellaria in the older species has also been employed by Pratt (1902) as a char- 

 acteristic of the genus in elaborating his key for the determination of the flukes. 

 Although typically a member of the genus Azygia, the present form would fall 

 in another genus according to the terms of that synopsis. No one who sees a 

 specimen or reviews the structure of this form can doubt its relationship; the 

 precise extent of the vitellaria is evidently a subordinate feature, and as such 

 of specific rank only. 



The follicles of the vitellaria are distinct, regularly oval bodies, lying in 

 two longitudinal rows on each side with a more or less conspicuous break oppo- 

 site the ovary between the anterior and posterior series. The follicles measure 

 from 0.06 to 0.07 by 0.03 to 0.04 mm. The symmetry of the rows is in places 

 interrupted by extra follicles, making at such points three rows of follicles 

 instead of two as usual. The ducts from the anterior and posterior series unite 

 opposite the ovary to form a common transverse duct which at the center of 

 the body joins its fellow from the opposite side. At the point of union there is a 

 small yolk reservoir. As already noted, this is included within the common 

 capsule which surrounds the ovary and is ordinarily not visible except in sec- 

 tions. Laurer's canal is present and opens on the dorsal surface just posterior 

 to the ovary. It does not have the enlargement ordinarily called a seminal 

 receptacle, but is usually somewhat coiled and lies on the left side of the ovary. 

 This may be an adaptation to the extreme variations in length so character- 

 istic of this worm. 



The eggs are small; an average of 50 measurements places their size at 48 

 by 27 fi, which is slightly larger and broader than those of A. tereticollis, accord- 

 ing to the measurements given by Looss (1894). 



The testes are oval bodies lying one directly behind the other and that 

 behind the ovary. The three organs are separated only very slightly from each 

 other. The outline of the testes is smooth and measures 0.42 to 0.46 by 0.59 

 to 0.6 mm. with the major axis transverse. One can usually distinguish that 

 the two are not equal in size. The coiled seminal vesicle and a poorly devel- 

 oped cirrus with prostate lie in a common connective tissue capsule, the cirrus; 

 pouch, which stands immediately anterior to the acetabulum. The pouch 

 measures about 0.23 by 0.17 mm. in diameter. It opens anterior to the metra- 

 term into the genital sinus already mentioned. 



One histological feature deserves consideration here because of its con- 

 spicuous character. In sections of Azygia sebago one notices certain muscle 

 elements which are so prominent and regular as to deserve almost the name of 

 a layer; they occur within the parenchyma, far removed from the usually rec- 

 ognized dermal layers and at a point where ordinarily one finds only scattered 



