if»ii| Watson: The Genus Gyrocotyle. 393 



by Lonnberg (181)1). There is here a doubling of layers, due to 

 folding on the ventral surface, and an increase in the inner trans- 

 verse layer to produce two "wing-muscles." Lonnberg 's tabula- 

 tion of the funnel muscles and their homologues in Gyrocotylt 

 urna the writer finds substantially correct for G. fimbriata. Here 

 as in the acetabulum the development has been mainly in the 

 inner transverse layer, and in the sagittal fibres. By means of 

 these a very effective sphincter is produced at the base of the 

 rosette. Posterior to the collar or "neck" (the region occupied 

 by this sphincter) and anterior to it near the canal opening, the 

 development of the transverse muscle layer is much reduced, 

 though still greater than in the body in general. 



Lonnberg concludes from the above described arrangement of 

 muscle layers that the rosette and canal were formed by a fold- 

 ing from the posterior extremity forward in the ventral surface. 

 This was first a furrow or trough, which functioned as a sucker, a 

 condition common among the lower cestodes; later the ventral 

 walls fused to form a tube, and finally only the most posterior 

 part of the tube functioned as an organ of attachment, its 

 anterior extremity remaining open as the present ventral open- 

 ing of the canal. Lonnberg hazards no opinion as to the signifi- 

 cance of this anterior canal opening. Observations on the 

 attached worm show that the mouth of the opening is always 

 closed while the rosette is attached to the mucosa. "When the 

 canal mouth opens, flaring out as in Spencer's figure 2, the hold 

 of the rosette loosens and the worm drops from the mucosa. 

 During attachment there is a series of waves of contraction, run- 

 ning from the margin of the rosette forward to the canal open- 

 ing. The whole posterior extremity thus forms a suction-cup of 

 high efficiency. The musculature of the ventral canal-opening, 

 developed from the peripheral muscles, is shown in plate 40. 

 figure 4-1. 



The finer structure of the muscles in Gyrocotyle is very 

 simple. The sagittal fibres (radial fibres of acetabulum and 

 rosette collar) are not aggregated into bundles but are simple 

 strands running through the body, distinguished from parenchy- 

 mal fibres by their size and also by the position of the nucleus 

 (pi. 42, fig. 57). This lies to one side of the fibre, forming a 



