AKT. 21. PARASITES OF SHAEKS AND SKATES LINTON. 17 



One conspictious feature in scoleces of certain cestodes, as for 

 example, CaUiohothrium^ mentioned by Zschokke ^ as characteristic 

 of Monorygma perfecfum^ that is the four muscular bands placed 

 transversely at the level of the boundary between the accessory suck- 

 ers and the bothria, seems to be entirely wanting. 



Diesing makes the presence of a myzorhynchus a generic character 

 of Monorygma. Zschokke does not mention this structure, although 

 his admirable account of this species does not include a detailed de- 

 scription of the histology of the scolex. As stated above I find what 

 I interpret as the rudiment of a myzorhynchus in the scolex of the 

 Alaska material. 



Strohile. — For a short distance back of the scolex there is no indi- 

 cation of segments, further than is shown by faint, transverse lines. 

 About 4 mm. back of the scolex the lateral margins are minutely but 

 regularly crenulate, and at a distance of 10 mm., definite segments 

 can be distinguished, with a length of 0.07 and a breadth of 3 mm. 

 For other dimensions, see foregoing measurements. The general 

 habit is rather broad, and, especially in the region of ripe segments, 

 thickish. Sections of proglottides, with uterus moderately filled with 

 ova, show the thickness to be about one-third the breadth. The lat- 

 eral margins of the proglottides are slightly rounded, and the pos- 

 terior margin projects but little. The genital pores are irregularly 

 alternate, and are placed near the anterior end of the proglottis, al- 

 most exactly on the lateral margin, but shown in sagittal sections to 

 be situated a little toward the ventral side. 



The cuticle consists of a dense inner layer, and a thicker outer layer 

 which abrades easily. The outer layer is difficult to interpret. I find 

 no trace of the stiff, slightly recurved bristles on the neck, nor of 

 the dense covering of papillae on other parts of the strobile, such as 

 are mentioned by Zschokke.^ The outer layer in longitudinal sec- 

 tions appears to be made up of short, blunt papillae, but these are 

 but sections of the fine transverse corrugations on the surface of the 

 strobile, which, it is true, simulate papillae. 



The fibers of the longitudinal muscles are rather slender, and 

 peculiar in that they are, for the most part, distinct, except at the 

 lateral margins, and in the neck, where there is a slight indication of 

 fascicles. The muscular layer is not sharply marked off from the 

 vitellaria on the one hand, and its fibers interpenetrate the subcuti- 

 cula on the other. Near the scolex the muscle fibers become larger 

 and more numerous and they encroach on the suiTounding tissue to 



« Recherch. sur la Structure Anatomique et Histologique des Cestodes, p. 285. 

 'Idem, p. 284. 



