1911] Watson: The Genus Gyrocotyle. 373 



is firmly attached by the terminal rosette, which is spread over 

 an area of ten to twelve millimeters in diameter. The folds of the 

 rosette fit over the vi.lli of the intestine. The canal opening (on 

 the ventral surface) is closed as long as the rose tte_ remains 

 attached. A series of waves of contraction passes from the 

 margin of the rosette toward the canal opening, during the 

 attachment of the rosette. The lateral frills are present even in 

 the most expanded state of the worm, constituting one-half of 

 the total width of the body. The acetabulum is very active, 

 thrusting itself backward, under, over or to the side of the body. 

 The whole worm contracts and expands frequently without any 

 apparent stimulus. The parasite is not easily affected by 

 mechanical stimuli under these conditions, but will contract if 

 exposed to direct sunlight, and is very sensitive to chemical 

 stimuli. The acetabulum has never been found attached, or in 

 any sense functioning as a sucker. This statement is borne out 

 by all investigators. 



Shortly after the death of the fish, the fluid intestinal con- 

 tents become thick and opaque, and the worm detaches itself and 

 contracts, losing its translucence and becoming creamy-white in 

 color. The region of the mucous membrane to which the rosette 

 has been attached is of a deep purplish red, and appears inflamed 

 after the rosette has detached itself. Many of the worms are 

 found in this opaque condition, and do not again become active. 

 From observations on the behavior of the attached specimens, and 

 from the fact that inactive specimens are found in all parts of 

 the intestinal tract, in the mouth and on the gills, it appears 

 fairly certain that the worm attempts to leave the dead host, and 

 very frequently succeeds in doing so. In one case, the worm was 

 found crawling up the first turn of the valve, when the intestine 

 was opened. The fact that specimens are so often found,, either 

 in the first or next to the last turn of the valve, also points to this 

 conclusion. Finally, the finding of a living specimen crawling 

 on the bottom of a jar of sea-water in which a Chimaera had 

 been placed, is fairly conclusive evidence that the worm occa- 

 sionally succeeds in escaping from its host. The parasite is never 

 found attached elsewhere than in the spiral valve. Spencer 

 (1889, p. 138) remarks in this connection: "The specimens 



