730 Henry B. Ward, 



the margin of the pore of somewhat regulär form which are pictured 

 and are designated as a proboscis, both by Spencer and by Watson. 

 In truth however this is in no sense a definite morpliological feature. 

 There are no special muscles nor even any increase in the thickness 

 of the ordinary muscle layers at this point. In highly contracted 

 specimens the muscles appear heavy and prominent because of the 

 contraction but in cases where the muscles are relaxed one finds in 

 a study of serial sections a perfectly uniform transition from the 

 body wall to that of the canal. The diiferent layers do not vary 

 perceptibly in thickness at the mouth of the canal. The so-called 

 proboscis is merely a hemorrhoidal puckering or evagination of the 

 canal wall under the pressure of powerful muscular contraction; 

 even tho somewhat regulär in form it has no independent structure 

 and no right to a specific designation. In the interest of morpho- 

 logical accuracy the term proboscis should be dropped. The inner 

 muscle layer of circular fibres dips down at the canal pore and 

 forms the coat which later is cut oif as the circular layer of the 

 canal. This is a prominent feature thru the entire length of the 

 canal; it is located at about 60 to 80 (j. from the lumen and forms 

 a loose band of 30 /u or more in width in which the fibres are 

 distinct, in general parallel, and extend in uninterrupted series 

 around the circle (Fig. 13). Towards the central part of the canal 

 this band becomes twice or three times as broad, it is also looser 

 and not quite so sharply limited. Where cut tangentially it appears 

 very broad and open, and here one can also detect a very delicate 

 layer of fibres at right angles to these circular fibres. The longi- 

 tudinal layer lies outside, i. e., further from the lumen of the canal 

 and is evidently of very minor functional importance. The highly 

 developed circular layer is a powerful sphincter muscle and its 

 functional value in closing the canal when the rosette is acting as 

 a sucker is too evident to need extended explanation. The special 

 outlet must make the action of the sucker more immediate than is 

 that of the ordinary imperforate cup-shaped acetabulum of trema- 

 todes and cestodes. The canal enters from the convex side as a 

 narrow slit at right angles to the surface of the body. The vertical 

 Stretch is only 0,4 mm long as it turns almost immediately and 

 proceeds posteriad and ventrad to the center of the rosette. Its 

 total length is about 1,5 to 2 mm. 



Near the extreme anterior end of the canal the lumen displays 

 a stellate form due to the folds in the wall. These folds are so 



